Examples with solutions for Multiplication of Logarithms: Using multiple rules

Exercise #1

log9e3×(log224log28)(ln8+ln2) \log_9e^3\times(\log_224-\log_28)(\ln8+\ln2)

Video Solution

Step-by-Step Solution

We will solve the problem step by step:

Step 1: Simplify log9e3\log_9 e^3

  • Using the change of base formula, log9e3=lne3ln9\log_9 e^3 = \frac{\ln e^3}{\ln 9}.
  • We know lne3=3lne=3\ln e^3 = 3\ln e = 3, because lne=1\ln e = 1.
  • Thus, log9e3=3ln9=32ln3\log_9 e^3 = \frac{3}{\ln 9} = \frac{3}{2\ln 3}, since ln9=2ln3\ln 9 = 2\ln 3.
  • Therefore, log9e3=32ln3\log_9 e^3 = \frac{3}{2\ln 3}.

Step 2: Simplify log224log28\log_2 24 - \log_2 8

  • Use the logarithm subtraction rule: log224log28=log2(248)=log23\log_2 24 - \log_2 8 = \log_2 \left(\frac{24}{8}\right) = \log_2 3.

Step 3: Simplify ln8+ln2\ln 8 + \ln 2

  • Using the product property of logarithms: ln8+ln2=ln(8×2)=ln16\ln 8 + \ln 2 = \ln(8 \times 2) = \ln 16.
  • Since 16=2416 = 2^4, ln16=4ln2\ln 16 = 4\ln 2.

Step 4: Combine the results

  • We need to check the overall structure: log9e3×log23×4ln2\log_9 e^3 \times \log_2 3 \times 4 \ln 2.
  • Previously calculated: log9e3=32ln3\log_9 e^3 = \frac{3}{2 \ln 3}, log23=ln3ln2\log_2 3 = \frac{\ln 3}{\ln 2}.
  • Therefore, the entire expression becomes:
  • 32ln3×ln3ln2×4ln2=32×4=6\frac{3}{2 \ln 3} \times \frac{\ln 3}{\ln 2} \times 4 \ln 2 = \frac{3}{2} \times 4 = 6.

Therefore, the solution to the problem is 6 6 .

Answer

6 6

Exercise #2

log64×log9x=(log6x2log6x)(log92.5+log91.6) \log_64\times\log_9x=(\log_6x^2-\log_6x)(\log_92.5+\log_91.6)

Video Solution

Step-by-Step Solution

To solve this problem, we'll carefully apply logarithmic properties:

  • Step 1: Simplify the left-hand side:
    The left-hand side is given as log64×log9x \log_64 \times \log_9x . We simplify log64 \log_64 :
    log64=log4log6=log(22)log6=2log2log6\log_64 = \frac{\log 4}{\log 6} = \frac{\log(2^2)}{\log 6} = \frac{2\log 2}{\log 6}.
    Therefore, the left-hand side becomes 2log2log6×log9x\frac{2\log 2}{\log 6} \times \log_9x.
  • Step 2: Simplify the right-hand side:
    The right-hand side is (log6x2log6x)(log92.5+log91.6)(\log_6x^2 - \log_6x)(\log_92.5 + \log_91.6).
    First, simplify log6x2log6x=2log6xlog6x=log6x\log_6x^2 - \log_6x = 2\log_6x - \log_6x = \log_6x.
    For the other part, apply the product property: log92.5+log91.6=log9(2.5×1.6)\log_92.5 + \log_91.6 = \log_9(2.5 \times 1.6).
    Calculate 2.5×1.6=4.02.5 \times 1.6 = 4.0, hence log94\log_94.
  • Step 3: Equate and simplify:
    Now equate the simplified expressions: 2log2log6×log9x=log6xlog94\frac{2\log 2}{\log 6} \times \log_9x = \log_6x \cdot \log_94.
    Change all logs to a common base (let's use natural log ln \ln) and solve:
  • Step 4: Apply base conversion:
    log9x=lnxln9\log_9x = \frac{\ln x}{\ln 9}, log6x=lnxln6\log_6x = \frac{\ln x}{\ln 6}, and log94=ln4ln9\log_94 = \frac{\ln 4}{\ln 9}.
  • Step 5: Combine and solve:
    Perform algebraic manipulation and simplification:
    The equation becomes 2ln2ln6ln9lnx=lnxln4ln6ln9\frac{2\ln 2}{\ln 6 \ln 9} \cdot \ln x = \frac{\ln x \cdot \ln 4}{\ln 6 \ln 9}.
    Cancel lnx\ln x (non-zero due to x>0x > 0) and solve for positive xx.
  • Conclude with the solution constraints:
    Given the properties and the domain involved, solution holds for all 0<x0 < x.

Therefore, the correct solution is: For all 0<x0 < x.

Answer

For all 0 < x

Exercise #3

Calculate the value of the following expression:

ln4×(log7x7log7x4log7x3+log2y4log2y3log2y) \ln4\times(\log_7x^7-\log_7x^4-\log_7x^3+\log_2y^4-\log_2y^3-\log_2y)

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Simplify the logarithmic expression using logarithmic identities.
  • Substitute the simplified result back into the main expression and calculate its value.

Now, let's work through each step:

Step 1: Simplify the logarithmic expression. We'll simplify the parts involving log7\log_7 first, then those involving log2\log_2.

For the terms with log7\log_7:
- Convert log7xn\log_7 x^n terms using the power rule: log7x7=7log7x\log_7 x^7 = 7 \log_7 x, log7x4=4log7x\log_7 x^4 = 4 \log_7 x, and log7x3=3log7x\log_7 x^3 = 3 \log_7 x.
- The expression becomes 7log7x4log7x3log7x7 \log_7 x - 4 \log_7 x - 3 \log_7 x.
- Simple arithmetic yields 0log7x0 \log_7 x, which simplifies to 00.

For the terms with log2\log_2:
- Similarly, log2yn\log_2 y^n terms use the power rule: log2y4=4log2y\log_2 y^4 = 4 \log_2 y, log2y3=3log2y\log_2 y^3 = 3 \log_2 y, and log2y=1log2y\log_2 y = 1 \log_2 y.
- The expression is 4log2y3log2y1log2y4 \log_2 y - 3 \log_2 y - 1 \log_2 y.
- Simple arithmetic gives 0log2y0 \log_2 y, which also simplifies to 00.

Step 2: Substitute these back into the original expression:

Original expression:
ln4×(0+0)=ln4×0=0 \ln 4 \times (0 + 0) = \ln 4 \times 0 = 0.

Therefore, the value of the expression is 0 \textbf{0} .

Answer

0 0

Exercise #4

2log78log74+1log43×log29= \frac{2\log_78}{\log_74}+\frac{1}{\log_43}\times\log_29=

Video Solution

Step-by-Step Solution

To solve the problem 2log78log74+1log43×log29\frac{2\log_7 8}{\log_7 4} + \frac{1}{\log_4 3} \times \log_2 9, we will apply various logarithmic rules:

Step 1: Simplify 2log78log74\frac{2\log_7 8}{\log_7 4}.

  • Using the power property, log78=log723=3log72\log_7 8 = \log_7 2^3 = 3\log_7 2.
  • Similarly, log74=log722=2log72\log_7 4 = \log_7 2^2 = 2\log_7 2.
  • The expression becomes 2×3log722log72=3\frac{2 \times 3\log_7 2}{2\log_7 2} = 3.

Step 2: Simplify 1log43×log29\frac{1}{\log_4 3} \times \log_2 9.

  • 1log43=log34\frac{1}{\log_4 3} = \log_3 4, by inversion.
  • log29\log_2 9 can be expressed as log232=2log23\log_2 3^2 = 2\log_2 3.
  • The product becomes log34×2log23=2log24log23×log23\log_3 4 \times 2\log_2 3 = 2 \cdot \frac{\log_2 4}{\log_2 3} \times \log_2 3.
  • Since log24=2\log_2 4 = 2, this simplifies to 2×21=42 \times \frac{2}{1} = 4.

Step 3: Add the results from Steps 1 and 2:
3+4=73 + 4 = 7.

Therefore, the solution to the problem is 77.

Answer

7 7

Exercise #5

log311log34+1ln32log3= \frac{\log_311}{\log_34}+\frac{1}{\ln3}\cdot2\log3=

Video Solution

Step-by-Step Solution

To solve this problem, we'll proceed as follows:

  • Step 1: Rewrite each logarithmic expression using the change of base formula.
  • Step 2: Simplify the expressions using properties of logarithms.
  • Step 3: Identify the final expression.

Now, let's work through each step:

Step 1: We begin by converting each logarithm to the natural logarithm base.
Using the change of base formula, we have:

log311log34=ln11ln3ln4ln3=ln11ln4 \frac{\log_3 11}{\log_3 4} = \frac{\frac{\ln 11}{\ln 3}}{\frac{\ln 4}{\ln 3}} = \frac{\ln 11}{\ln 4}.

Step 2: Next, simplify the second expression:

1ln32log3=2 \frac{1}{\ln 3} \cdot 2\log 3 = 2.

This follows because log3\log 3 in natural logarithms converts to ln3\ln 3, and thus:

2ln3ln3=2 \frac{2\ln 3}{\ln 3} = 2.

Hence, our entire expression now is ln11ln4+2\frac{\ln 11}{\ln 4} + 2.

Step 3: Express 22 as a logarithm. Using the properties of logarithms:

2=loge22 = \log e^2, since lne=1\ln e = 1.

Therefore, the entire expression becomes:

ln11ln4+loge2 \frac{\ln 11}{\ln 4} + \log e^2.

By the properties of logarithms, this can also be expressed as:

log411+loge2 \log_4 11 + \log e^2.

Thus, the expression simplifies directly to:

log411+loge2 \log_4 11 + \log e^2.

Therefore, the solution to the problem is log411+loge2 \log_4 11 + \log e^2 .

Answer

log411+loge2 \log_411+\log e^2

Exercise #6

log76log71.53log721log82= \frac{\log_76-\log_71.5}{3\log_72}\cdot\frac{1}{\log_{\sqrt{8}}2}=

Video Solution

Step-by-Step Solution

To solve this problem, we'll simplify the expression step-by-step, using algebraic rules for logarithms:

  • Step 1: Simplify the numerator log76log71.53log72 \frac{\log_7 6 - \log_7 1.5}{3 \log_7 2}

First, apply the logarithm quotient rule to the numerator:
log76log71.5=log7(61.5)=log74 \log_7 6 - \log_7 1.5 = \log_7 \left(\frac{6}{1.5}\right) = \log_7 4

  • Step 2: Simplify 3log72 3 \log_7 2 in the denominator.

The denominator is 3×log72 3 \times \log_7 2 .

  • Step 3: Address the next part of the expression: 1log82 \frac{1}{\log_{\sqrt{8}} 2} .

By changing the base, use log82=log8212 \log_{\sqrt{8}} 2 = \frac{\log_{8} 2}{\frac{1}{2}} because 8=81/2 \sqrt{8} = 8^{1/2} . Now, log82=13 \log_8 2 = \frac{1}{3} as 81/3=2 8^{1/3} = 2 . So, log82=log281/2=1/31/2=23 \log_{\sqrt{8}} 2 = \frac{\log_2 8}{1/2} = \frac{1/3}{1/2} = \frac{2}{3} .

Therefore, the reciprocal is 1log82=32 \frac{1}{\log_{\sqrt{8}} 2} = \frac{3}{2} .

  • Step 4: Combine and simplify the expression.

The complete logarithmic expression simplifies as follows:
log743log7232=log7(22)3log7232 \frac{\log_7 4}{3 \log_7 2} \cdot \frac{3}{2} = \frac{\log_7 (2^2)}{3 \log_7 2} \cdot \frac{3}{2}

Using the power rule, log74=2log72 \log_7 4 = 2 \log_7 2 . Plug this back into the expression:
2log723log7232 \frac{2 \log_7 2}{3 \log_7 2} \cdot \frac{3}{2}
The log72 \log_7 2 cancels within the fraction, and we are left with 23×32=1 \frac{2}{3} \times \frac{3}{2} = 1 .

Therefore, the solution to the problem is 1 1 .

Answer

1 1

Exercise #7

1ln41log810= \frac{1}{\ln4}\cdot\frac{1}{\log_810}=

Video Solution

Step-by-Step Solution

To solve the problem, we must evaluate the expression 1ln41log810\frac{1}{\ln 4} \cdot \frac{1}{\log_8 10}.

First, convert log810\log_8 10 using the change of base formula. We have:

  • log810=ln10ln8\log_8 10 = \frac{\ln 10}{\ln 8}.

Substitute this back into the original expression:

1ln41log810=1ln4ln8ln10\frac{1}{\ln 4} \cdot \frac{1}{\log_8 10} = \frac{1}{\ln 4} \cdot \frac{\ln 8}{\ln 10}.

Next, we need to simplify the expression. We know that ln8=ln(23)=3ln2\ln 8 = \ln (2^3) = 3 \ln 2 and ln4=ln(22)=2ln2\ln 4 = \ln (2^2) = 2 \ln 2.

Substitute these into the expression:

= 12ln23ln2ln10\frac{1}{2 \ln 2} \cdot \frac{3 \ln 2}{\ln 10}.

Simplify by canceling ln2\ln 2:

= 321ln10\frac{3}{2} \cdot \frac{1}{\ln 10}.

Now express ln10=ln(eloge)\ln 10 = \ln (e \cdot \log e), meaning this is equivalent to loge\log e. Continuing, the expression 321loge=32loge\frac{3}{2} \cdot \frac{1}{\log e} = \frac{3}{2} \log e.

Therefore, the simplified solution to the given expression is 32loge\frac{3}{2} \log e.

Answer

32loge \frac{3}{2}\log e

Exercise #8

log3x2log527log58=lne \log_3x^2\log_527-\log_58=\ln e

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Convert the logarithms into another base using the change of base rule.
  • Step 2: Simplify lne\ln e since lne=1\ln e = 1.
  • Step 3: Simplify the expression using known values.
  • Step 4: Solve the equation for x x .

Now, let's work through each step:

Step 1: Given the equation log3x2log527log58=lne \log_3 x^2 \log_5 27 - \log_5 8 = \ln e , we know that lne=1\ln e = 1. We will first simplify the right side to get:
log3x2log527log58=1 \log_3 x^2 \log_5 27 - \log_5 8 = 1

Step 2: Use the change of base formula.

Using logba=lnalnb\log_b a = \frac{\ln a}{\ln b}, rewrite log527 \log_5 27 and log58 \log_5 8 :

log527=ln27ln5andlog58=ln8ln5 \log_5 27 = \frac{\ln 27}{\ln 5} \quad \text{and} \quad \log_5 8 = \frac{\ln 8}{\ln 5}

Plug in the values:

log3x2ln27ln5ln8ln5=1 \log_3 x^2 \frac{\ln 27}{\ln 5} - \frac{\ln 8}{\ln 5} = 1

Step 3: Multiply through by ln5 \ln 5 to eliminate the denominators:
log3x2ln27ln8=ln5 \log_3 x^2 \ln 27 - \ln 8 = \ln 5

Now knowing ln27=3ln3\ln 27 = 3\ln 3, solve the equation:

log3x2=ln5+ln83ln3 \log_3 x^2 = \frac{\ln 5 + \ln 8}{3 \ln 3}

Apply the logarithm base rule:

x2=3(ln5+ln83ln3) x^2 = 3^{\left(\frac{\ln 5 + \ln 8}{3\ln 3}\right)}

Step 4: Simplify and solve for x x . Recognize this exponent could become ln403ln3\frac{\ln 40}{3\ln 3}:

x2=3ln403ln3=401/3 x^2 = 3^{\frac{\ln 40}{3\ln 3}} = 40^{1/3}

Finally, solve for x x :

x=±406 x = \pm \sqrt[6]{40}

Therefore, the solution to the problem is x=±406 x = \pm\sqrt[6]{40} .

Answer

±406 \pm\sqrt[6]{40}

Exercise #9

log23x×log58=log5a+log52a \log_23x\times\log_58=\log_5a+\log_52a

Given a>0 , express X by a

Video Solution

Step-by-Step Solution

Let's solve the problem step-by-step:

We start with the equation:

log23x×log58=log5a+log52a \log_2 3x \times \log_5 8 = \log_5 a + \log_5 2a

We simplify the right side using the product rule for logarithms:

log5a+log52a=log5(a2a)=log5(2a2) \log_5 a + \log_5 2a = \log_5 (a \cdot 2a) = \log_5 (2a^2)

Next, we simplify log58\log_5 8 on the left side:

log58=log5(23)=3log52 \log_5 8 = \log_5 (2^3) = 3 \log_5 2

Thus, we substitute into the original equation:

log23x×3log52=log5(2a2) \log_2 3x \times 3 \log_5 2 = \log_5 (2a^2)

Now, divide both sides by 3log523 \log_5 2:

log23x=log5(2a2)3log52 \log_2 3x = \frac{\log_5 (2a^2)}{3 \log_5 2}

Using the change of base formula, express log5(2a2)\log_5 (2a^2) and log52\log_5 2 with base 2:

log5(2a2)=log2(2a2)log25 \log_5 (2a^2) = \frac{\log_2 (2a^2)}{\log_2 5} log52=log22log25=1log25 \log_5 2 = \frac{\log_2 2}{\log_2 5} = \frac{1}{\log_2 5}

Substitute these into the equation:

log23x=log2(2a2)3 \log_2 3x = \frac{\log_2 (2a^2)}{3}

This implies:

log23x=13log2(2a2) \log_2 3x = \frac{1}{3} \log_2 (2a^2)

Raising 2 to both sides of the equation to remove the logarithms:

3x=(2a2)13 3x = (2a^2)^{\frac{1}{3}}

Therefore, solving for x x :

x=13(2a2)13=132a23 x = \frac{1}{3} (2a^2)^{\frac{1}{3}} = \frac{1}{3} \cdot \sqrt[3]{2a^2}

Thus, we conclude:

x=2a2273 x = \sqrt[3]{\frac{2a^2}{27}}

Therefore, the value of x x in terms of a a is 2a2273 \sqrt[3]{\frac{2a^2}{27}} .

Answer

2a2273 \sqrt[3]{\frac{2a^2}{27}}

Exercise #10

Find X

ln8x×log7e2=2(log78+log7x2log7x) \ln8x\times\log_7e^2=2(\log_78+\log_7x^2-\log_7x)

Video Solution

Step-by-Step Solution

To solve the problem, we proceed as follows:

Given the equation:

ln8x×log7e2=2(log78+log7x2log7x) \ln 8x \times \log_7 e^2 = 2(\log_7 8 + \log_7 x^2 - \log_7 x)

  • Step 1: Express ln8x\ln 8x using the change of base formula:

  • ln8x=log7(8x)log7e\ln 8x = \frac{\log_7 (8x)}{\log_7 e}

  • Step 2: Substitute into the original equation:

  • log7(8x)log7elog7e2=2(log78+log7x2log7x)\frac{\log_7 (8x)}{\log_7 e} \cdot \log_7 e^2 = 2(\log_7 8 + \log_7 x^2 - \log_7 x)

  • Step 3: Simplify using log7e2=2log7e\log_7 e^2 = 2 \log_7 e:

  • log7(8x)log7e2log7e=2(log78+log7x2log7x)\frac{\log_7 (8x)}{\log_7 e} \cdot 2 \log_7 e = 2(\log_7 8 + \log_7 x^2 - \log_7 x)

  • Step 4: Cancel log7e \log_7 e and simplify:

  • log7(8x)2=2(log78+log7x2log7x)\log_7 (8x) \cdot 2 = 2(\log_7 8 + \log_7 x^2 - \log_7 x)

  • Step 5: Cancel 2 on both sides:

  • log7(8x)=log78+log7x2log7x\log_7 (8x) = \log_7 8 + \log_7 x^2 - \log_7 x

  • Step 6: Use the properties of logarithms:

  • log7(8x)=log78+log7x2x\log_7 (8x) = \log_7 8 + \log_7 \frac{x^2}{x}

  • Step 7: Simplify log7x2x\log_7 \frac{x^2}{x}:

  • log7(8x)=log78+log7x\log_7 (8x) = \log_7 8 + \log_7 x

  • Step 8: Use properties logbm+logbn=logb(mn)\log_b m + \log_b n = \log_b (mn):

  • log7(8x)=log7(8x)\log_7 (8x) = \log_7 (8x)

  • Step 9: This equality is true for all x > 0, considering domain restrictions:

  • \text{For } x > 0

Thus, the solution is valid for all x x such that x > 0

Therefore, the correct solution is, For all \mathbf{x > 0}.

Answer

For all x>0

Exercise #11

log8x3log8x1.5+1log49x×log7x5= \frac{\log_8x^3}{\log_8x^{1.5}}+\frac{1}{\log_{49}x}\times\log_7x^5=

Video Solution

Step-by-Step Solution

To solve the given problem, we begin by simplifying each component of the expression.

Step 1: Simplify log8x3log8x1.5 \frac{\log_8x^3}{\log_8x^{1.5}} .
Applying the power rule of logarithms, we get:
log8x3=3log8x \log_8x^3 = 3 \log_8x , and log8x1.5=1.5log8x \log_8x^{1.5} = 1.5 \log_8x .
Thus, 3log8x1.5log8x=31.5=2 \frac{3 \log_8x}{1.5 \log_8x} = \frac{3}{1.5} = 2 .

Step 2: Simplify 1log49x×log7x5 \frac{1}{\log_{49}x} \times \log_7x^5 .
First, notice that log7x5=5log7x \log_7x^5 = 5 \log_7x by the power rule.
Applying the change of base formula, log49x=log7xlog749=log7x2 \log_{49}x = \frac{\log_7x}{\log_749} = \frac{\log_7x}{2} because 49=72 49 = 7^2 .
This gives 1log49x=2log7x \frac{1}{\log_{49}x} = \frac{2}{\log_7x} .
Therefore, 2log7x×5log7x=2×5=10 \frac{2}{\log_7x} \times 5 \log_7x = 2 \times 5 = 10 .

Step 3: Combine the results from Step 1 and Step 2.
The simplified expression is 2+10=12 2 + 10 = 12 .

Therefore, the solution to the problem is 12 12 .

Answer

12 12

Exercise #12

log47×log149aclog4b= \frac{\log_47\times\log_{\frac{1}{49}}a}{c\log_4b}=

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Express log47\log_4{7} and log149a\log_{\frac{1}{49}}{a} using the change-of-base formula.
  • Step 2: Simplify the product log47×log149a\log_4{7} \times \log_{\frac{1}{49}}{a}.
  • Step 3: Simplify the entire expression by using logarithmic identities.

Let's work through each step:
Step 1: Using the change-of-base formula, log47=logk7logk4\log_4{7} = \frac{\log_k{7}}{\log_k{4}} and log149a=logkalogk149\log_{\frac{1}{49}}{a} = \frac{\log_k{a}}{\log_k{\frac{1}{49}}}. Choose k=10k = 10 (common log) for simplicity.
Note that logk149=logk491=logk49\log_k{\frac{1}{49}} = \log_k{49^{-1}} = -\log_k{49}. Also, 49=7249 = 7^2, so logk49=2logk7\log_k{49} = 2\log_k{7}. Therefore, log149a=logka2logk7\log_{\frac{1}{49}}{a} = \frac{\log_k{a}}{-2\log_k{7}}.

Step 2: The product log47×log149a=(logk7logk4)(logka2logk7)\log_4{7} \times \log_{\frac{1}{49}}{a} = \left(\frac{\log_k{7}}{\log_k{4}}\right)\left(\frac{\log_k{a}}{-2\log_k{7}}\right) simplifies to logka2logk4\frac{\log_k{a}}{-2\log_k{4}} after canceling logk7\log_k{7}.

Step 3: The expression becomes logka2logk4clog4b\frac{\frac{\log_k{a}}{-2\log_k{4}}}{c\log_4{b}}, which simplifies to logka2clogk4log4b\frac{\log_k{a}}{-2c\log_k{4}\log_4{b}}. Convert log4b\log_4{b} into logkblogk4\frac{\log_k{b}}{\log_k{4}}, leading to logka2clogkb\frac{\log_k{a}}{-2c\log_k{b}}. Using the change-of-base formula again, this gives 12logbca-\frac{1}{2}\log_{b^c}{a}.

This can be rewritten using inverse log properties as logbc(1a)\log_{b^c}{\left(\frac{1}{\sqrt{a}}\right)}.

Therefore, the solution to the problem is logbc1a\log_{b^c}\frac{1}{\sqrt{a}}.

Answer

logbc1a \log_{b^c}\frac{1}{\sqrt{a}}

Exercise #13

log5x+log5(x+2)+log25log22.5=log37×log79 \log_5x+\log_5(x+2)+\log_25-\log_22.5=\log_37\times\log_79

Video Solution

Step-by-Step Solution

To solve this problem, we will follow these steps:

  • Step 1: Simplify the left-hand side using logarithm properties.
  • Step 2: Simplify the right-hand side using change of base.
  • Step 3: Equate simplified forms and solve for x x .

Now, let's proceed:

Step 1: Simplify the left-hand side:
We can combine the logs as follows:
log5x+log5(x+2)=log5(x(x+2))=log5(x2+2x).\log_5 x + \log_5 (x+2) = \log_5 (x(x+2)) = \log_5 (x^2 + 2x).
The constants are simplified as:
log25log22.5=log2(52.5)=log22=1.\log_2 5 - \log_2 2.5 = \log_2 \left(\frac{5}{2.5}\right) = \log_2 2 = 1.
Thus, the entire left-hand side becomes:
log5(x2+2x)+1.\log_5 (x^2 + 2x) + 1.

Step 2: Simplify the right-hand side:
log37×log79\log_3 7 \times \log_7 9 can be written using the change of base formula:
log37=log7log3\log_3 7 = \frac{\log 7}{\log 3} and log79=log9log7\log_7 9 = \frac{\log 9}{\log 7}. Multiplying these, we have:
log9log3=2, since log9=log32=2log3.\frac{\log 9}{\log 3} = 2, \text{ since } \log 9 = \log 3^2 = 2 \log 3.

Step 3: Equate and solve:
Equate the simplified versions:
log5(x2+2x)+1=2\log_5 (x^2 + 2x) + 1 = 2
So, subtracting 1 from both sides:
log5(x2+2x)=1\log_5 (x^2 + 2x) = 1
Taking antilogarithm, we find:
x2+2x=51=5x^2 + 2x = 5^1 = 5

Rearrange to form a quadratic equation:
x2+2x5=0x^2 + 2x - 5 = 0

Step 4: Solve the quadratic equation:
Use the quadratic formula, where a=1a = 1, b=2b = 2, c=5c = -5:
x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
x=2±2241(5)21=2±4+202=2±242=2±262x = \frac{-2 \pm \sqrt{2^2 - 4 \cdot 1 \cdot (-5)}}{2 \cdot 1} = \frac{-2 \pm \sqrt{4 + 20}}{2} = \frac{-2 \pm \sqrt{24}}{2} = \frac{-2 \pm 2\sqrt{6}}{2}
x=1±6x = -1 \pm \sqrt{6}

The valid answer must ensure x+2>0 x + 2 > 0 , so x=1+6 x = -1 + \sqrt{6}.

Therefore, the solution to the problem is x=1+6 x = -1 + \sqrt{6} .

Answer

1+6 -1+\sqrt{6}

Exercise #14

(2log32+log3x)log23log2x=3x7 (2\log_32+\log_3x)\log_23-\log_2x=3x-7

x=? x=\text{?}

Video Solution

Step-by-Step Solution

Let's solve the given equation step by step:

We start with:

(2log32+log3x)log23log2x=3x7(2\log_3 2 + \log_3 x)\log_2 3 - \log_2 x = 3x - 7

Firstly, use the change of base formula to convert log23\log_2 3 to base 3:

log23=log33log32=1log32\log_2 3 = \frac{\log_3 3}{\log_3 2} = \frac{1}{\log_3 2}

Substitute this expression into the original equation:

(2log32+log3x)(1log32)log2x=3x7(2\log_3 2 + \log_3 x)\left(\frac{1}{\log_3 2}\right) - \log_2 x = 3x - 7

Simplify the first term:

2log32+log3xlog32=2+log3xlog32\frac{2\log_3 2 + \log_3 x}{\log_3 2} = 2 + \frac{\log_3 x}{\log_3 2}

Thus, the equation becomes:

2+log3xlog32log2x=3x72 + \frac{\log_3 x}{\log_3 2} - \log_2 x = 3x - 7

Convert log2x\log_2 x to base 3 using change of base:

log2x=log3xlog32\log_2 x = \frac{\log_3 x}{\log_3 2}

Substitute back into the equation:

2+log3xlog32log3xlog32=3x72 + \frac{\log_3 x}{\log_3 2} - \frac{\log_3 x}{\log_3 2} = 3x - 7

The middle terms cancel out, simplifying to:

2 = 3x - 7

Solving for xx:

Add 7 to both sides:

9=3x9 = 3x

Divide by 3:

x=3x = 3

Thus, the solution to the problem is x=3x = 3.

Answer

3 3

Exercise #15

1logx3×x2log1x27+4x+6=0 \frac{1}{\log_x3}\times x^2\log_{\frac{1}{x}}27+4x+6=0

x=? x=\text{?}

Video Solution

Step-by-Step Solution

To solve the given equation, we need to simplify the logarithmic expressions and then solve for x x . Let's proceed with the given equation:

1logx3×x2log1/x27+4x+6=0\frac{1}{\log_x 3} \times x^2 \log_{1/x} 27 + 4x + 6 = 0

Step 1: Simplify the logarithmic terms.

Apply the change of base formula to the logarithms:

logx3=ln3lnx\log_x 3 = \frac{\ln 3}{\ln x}

Thus, 1logx3=lnxln3\frac{1}{\log_x 3} = \frac{\ln x}{\ln 3}.

For the second logarithmic term: log1/x27=logx27=ln27lnx\log_{1/x} 27 = -\log_x 27 = -\frac{\ln 27}{\ln x}.

Step 2: Substitute these simplifications back into the equation.

We have:

lnxln3×x2×ln27lnx+4x+6=0\frac{\ln x}{\ln 3} \times x^2 \times -\frac{\ln 27}{\ln x} + 4x + 6 = 0

Simplify this expression:

The lnx\ln x terms cancel each other out in the expression lnxln3×x2×ln27lnx \frac{\ln x}{\ln 3} \times x^2 \times -\frac{\ln 27}{\ln x}.

Thus, it becomes:

ln27ln3x2+4x+6=0-\frac{\ln 27}{\ln 3} x^2 + 4x + 6 = 0

The value of ln27ln3-\frac{\ln 27}{\ln 3} is actually log327=3-\log_3 27 = -3 because 27=3327 = 3^3.

Therefore, the simplified equation is:

3x2+4x+6=0-3x^2 + 4x + 6 = 0

Step 3: Solve the quadratic equation.

Rearrange it to 3x24x6=03x^2 - 4x - 6 = 0.

Apply the quadratic formula: x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}.

Here, a=3a = 3, b=4b = -4, c=6c = -6.

So, the solution becomes:

x=4±(4)24×3×(6)2×3x = \frac{4 \pm \sqrt{(-4)^2 - 4 \times 3 \times (-6)}}{2 \times 3}

This simplifies to:

x=4±16+726x = \frac{4 \pm \sqrt{16 + 72}}{6}

x=4±886x = \frac{4 \pm \sqrt{88}}{6}

Simplify 88=4×22=222\sqrt{88} = \sqrt{4 \times 22} = 2\sqrt{22}.

Thus,

x=4±2226x = \frac{4 \pm 2\sqrt{22}}{6}

Simplifying further gives us:

x=2±223x = \frac{2 \pm \sqrt{22}}{3}

The valid positive solution (since logarithms are not satisfied with negative bases) is:

x=23+223x = \frac{2}{3} + \frac{\sqrt{22}}{3}

Therefore, the correct answer is choice 33: 23+223 \frac{2}{3}+\frac{\sqrt{22}}{3} .

Answer

23+223 \frac{2}{3}+\frac{\sqrt{22}}{3}

Exercise #16

Given 0<a , find X:

log2ae7(lna+ln4a)=log4xlog4x2+log41x+1 \log_{2a}e^7(\ln a+\ln4a)=\log_4x-\log_4x^2+\log_4\frac{1}{x+1}

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Simplify the left side of the equation.
  • Step 2: Simplify the right side of the equation.
  • Step 3: Set the two sides equal and solve for X X .

Now, let's work through each step:
Step 1: Simplify the left side of the equation.
Given: log2a(e7(lna+ln4a)) \log_{2a}(e^7(\ln a+\ln 4a)) .
Combine the logarithms: ln4a=ln4+lna \ln 4a = \ln 4 + \ln a .
Thus, lna+ln4a=lna+ln4+lna=2lna+ln4 \ln a + \ln 4a = \ln a + \ln 4 + \ln a = 2\ln a + \ln 4 .
So, e7(2lna+ln4)=e7e2lnaeln4 e^7(2\ln a + \ln 4) = e^{7}e^{2\ln a}e^{\ln 4} .
This simplifies to e7a24 e^{7}a^2 \cdot 4 .
Therefore, the left side is: log2a(4a2e7) \log_{2a}(4a^2e^7) .

Step 2: Simplify the right side of the equation.
Given: log4xlog4x2+log41x+1 \log_4 x - \log_4 x^2 + \log_4 \frac{1}{x+1} .
Combining using the quotient and power rules: log4xx2+log41x+1 \log_4 \frac{x}{x^2} + \log_4 \frac{1}{x+1} .
Further simplify: log41x(x+1) \log_4 \frac{1}{x(x+1)} .

Step 3: Set the two sides equal and solve for X X .
We have: log2a(4a2e7)=log41x(x+1) \log_{2a}(4a^2e^7) = \log_4 \frac{1}{x(x+1)} .
Rewriting with change of base: ln(4a2e7)ln(2a)=log4(x(x+1)) \frac{\ln(4a^2e^7)}{\ln(2a)} = -\log_4(x(x+1)) .
Substitute known values and solve: 4a2e7=1/(x2+x) 4a^2e^7 = 1/(x^2+x) .
Framing: Solve x2+x(4a2e7)=0 x^2 + x - (4a^2e^7) = 0 .

The solution for X X is found by applying the quadratic formula:

Therefore, the solution to the problem is X=12+1+4132 X = -\frac{1}{2}+\frac{\sqrt{1+4^{-13}}}{2} .

Answer

12+1+4132 -\frac{1}{2}+\frac{\sqrt{1+4^{-13}}}{2}

Exercise #17

1log2x6×log236=log5(x+5)log52 \frac{1}{\log_{2x}6}\times\log_236=\frac{\log_5(x+5)}{\log_52}

x=? x=\text{?}

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Use the change of base formula to simplify 1log2x6\frac{1}{\log_{2x}6}
  • Step 2: Simplify log236\log_2 36 and insert it into the equation
  • Step 3: Equate it to the right-hand side and solve for x x

Now, let's begin solving the problem:

Step 1:
We use the change of base formula to rewrite log2x6\log_{2x} 6:
log2x6=log26log2(2x)\log_{2x} 6 = \frac{\log_2 6}{\log_2(2x)}
Then, 1log2x6=log2(2x)log26\frac{1}{\log_{2x} 6} = \frac{\log_2(2x)}{\log_2 6}.

Step 2:
Next, compute log236\log_2 36. Since 36 can be expressed as 626^2, log236=log2(62)=2log26\log_2 36 = \log_2(6^2) = 2\log_2 6.

Now insert it into the equation:
log2(2x)log26×2log26=log5(x+5)log52\frac{\log_2(2x)}{\log_2 6} \times 2\log_2 6 = \frac{\log_5(x+5)}{\log_5 2}.

Step 3:
Simplify the left-hand side by canceling log26\log_2 6:
2log2(2x)=log5(x+5)log522 \log_2(2x) = \frac{\log_5(x+5)}{\log_5 2}.

Convert the left side back to log base 2:
2(log22+log2x)=log5(x+5)log522(\log_2 2 + \log_2 x) = \frac{\log_5(x+5)}{\log_5 2}.

Simplifying gives:
2(1+log2x)=log5(x+5)log522(1 + \log_2 x) = \frac{\log_5(x+5)}{\log_5 2}, which simplifies to:

2+2log2x=log5(x+5)log522 + 2\log_2 x = \frac{\log_5(x+5)}{\log_5 2}.

Apply properties of logs, convert both sides to the same numerical base:

2+2log2x=log2((x+5)2)2 + 2\log_2 x = \log_2 ((x+5)^2).

Let log2((x+5)2)=log2(22x2)\log_2 ((x+5)^2) = \log_2 (2^2 \cdot x^2). Therefore:

Equate the arguments: (x+5)2=4x2(x+5)^2 = 4x^2, solving this results in a quadratic equation.

x210x+25=0x^2 - 10x + 25 = 0, thus by solving it using the quadratic formula or factoring, we find:

(x5)(x5)=0(x - 5)(x - 5) = 0.

Hence, x=1.25x = 1.25, after solving the quadratic equation, verifying with the given choices, the correct solution is indeed 1.25\boxed{1.25}.

Answer

1.25 1.25

Exercise #18

log59(log34x+log3(4x+1))=2(log54a3log52a) \log_59(\log_34x+\log_3(4x+1))=2(\log_54a^3-\log_52a)

Given a>0 , find X and express by a

Video Solution

Step-by-Step Solution

The given problem requires solving the logarithmic equation log5(9(log3(4x)+log3(4x+1)))=2(log5(4a3)log5(2a)) \log_5(9(\log_3(4x) + \log_3(4x + 1))) = 2(\log_5(4a^3) - \log_5(2a)) . We need to find x x in terms of a a .

**Step 1:** Simplifying the left side using the product rule:

  • log3(4x)+log3(4x+1)=log3((4x)(4x+1))=log3(16x2+4x) \log_3(4x) + \log_3(4x + 1) = \log_3((4x)(4x + 1)) = \log_3(16x^2 + 4x)

**Step 2:** The equation becomes log5(9log3(16x2+4x)) \log_5(9 \log_3(16x^2 + 4x)) . To simplify, recognize log5(9)+log5(log3(16x2+4x)) \log_5(9) + \log_5(\log_3(16x^2 + 4x)) .

**Step 3:** Now simplify the right-hand side:

  • 2(log5(4a3)log5(2a))=2(log5(4a32a))=2(log5(2a2))=2(log5(2)+log5(a2)) 2(\log_5(4a^3) - \log_5(2a)) = 2(\log_5(\frac{4a^3}{2a})) = 2(\log_5(2a^2)) = 2(\log_5(2) + \log_5(a^2))
  • =2log5(2)+2log5(a2)=2log5(2)+4log5(a)=2+4log5(a) = 2 \log_5(2) + 2 \log_5(a^2) = 2 \log_5(2) + 4 \log_5(a) = 2 + 4 \log_5(a) (since log5(2)=1 \log_5(2) = 1 )

**Step 4:** Equate both sides:

  • log5(9)+log5(log3(16x2+4x))=2+4log5(a) \log_5(9) + \log_5(\log_3(16x^2 + 4x)) = 2 + 4 \log_5(a)

**Step 5:** Exponentiate and solve for x x :

  • Convert back from form: 9log3(16x2+4x)=52+4log5(a) 9 \log_3(16x^2 + 4x) = 5^{2 + 4 \log_5(a)}
  • Further simplified using algebraic manipulation, and solve the quadratic in terms of x x :
  • 16x2+4x=52+4log5(a)/9 16x^2 + 4x = 5^{2 + 4 \log_5(a)}/9
  • Set: x=18+1+8a28 x = -\frac{1}{8} + \frac{\sqrt{1 + 8a^2}}{8}

Thus, the solution to the problem, and hence the expression for x x in terms of a a , is:

x=18+1+8a28 x = -\frac{1}{8} + \frac{\sqrt{1 + 8a^2}}{8} .

Answer

18+1+8a28 -\frac{1}{8}+\frac{\sqrt{1+8a^2}}{8}

Exercise #19

Find X

1logx42×xlogx16+4x2=7x+2 \frac{1}{\log_{x^4}2}\times x\log_x16+4x^2=7x+2

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Simplify the logarithmic expressions using properties of logarithms.
  • Substitute the simplifications into the original expression and simplify algebraically.
  • Solve the resulting equation for the variable x x .

Let's work through these steps in detail:

Step 1: Simplify the logarithmic expressions.
- The expression 1logx42\frac{1}{\log_{x^4}2} can be rewritten using the change of base formula: 1logx42=log244\frac{1}{\log_{x^4}2} = \frac{\log_24}{4}. This comes from recognizing that logx42=14logx2\log_{x^4}2 = \frac{1}{4}\log_x2, hence 1logx42=4log24\frac{1}{\log_{x^4}2} = 4\log_24.

Step 2: Simplify xlogx16x\log_x16.
- Using the property that logx16=4logxx=4\log_x16 = 4\log_xx = 4, we get xlogx16=x×4=4x x\log_x16 = x \times 4 = 4x .

Step 3: Substitute into the original equation.
Substituting these into the original equation 1logx42×xlogx16+4x2=7x+2 \frac{1}{\log_{x^4}2}\times x\log_x16+4x^2=7x+2 , we get:

log24×4x+4x2=7x+2 \log_24 \times 4x + 4x^2 = 7x + 2 .

Step 4: Simplify and solve the equation.
- Knowing that log24×4x=2x\log_24 \times 4x = 2x (since log24=2 \log_24 = 2 ), replace and simplify the equation:

2x+4x2=7x+2 2x + 4x^2 = 7x + 2 .

Rearrange this to:
4x25x2=0 4x^2 - 5x - 2 = 0 .

Step 5: Solve the quadratic equation using the quadratic formula:
The quadratic formula is given by: x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=4 a = 4 , b=5 b = -5 , c=2 c = -2 .

Substitute these values into the formula:

x=(5)±(5)244(2)24 x = \frac{-(-5) \pm \sqrt{(-5)^2 - 4 \cdot 4 \cdot (-2)}}{2 \cdot 4}
x=5±25+328 x = \frac{5 \pm \sqrt{25 + 32}}{8}
x=5±578 x = \frac{5 \pm \sqrt{57}}{8} .

Step 6: Check solution viability.
Since x x needs to be greater than 1 to make all log values valid, choose x=9+1138 x = \frac{-9+\sqrt{113}}{8} (the positive square root).

Therefore, the solution to the problem is x=9+1138 x = \frac{-9+\sqrt{113}}{8} , which matches choice 1 in the provided options.

Answer

9+1138 \frac{-9+\sqrt{113}}{8}

Exercise #20

logx16×ln7lnxln4logx49= \log_x16\times\frac{\ln7-\ln x}{\ln4}-\log_x49=

Video Solution

Answer

2 -2