Examples with solutions for Rules of Logarithms Combined: Using multiple rules

Exercise #1

log4x+log2log9=log24 \log4x+\log2-\log9=\log_24

?=x

Video Solution

Step-by-Step Solution

To solve the equation log4x+log2log9=log24\log 4x + \log 2 - \log 9 = \log_2 4, we will follow these steps:

  • Step 1: Simplify the left side using logarithmic properties
  • Step 2: Convert the right side using change of base
  • Step 3: Equate the simplified expressions and solve for xx

Step 1: Simplify the left side:

The left side log4x+log2log9\log 4x + \log 2 - \log 9 can be combined using the properties of logarithms:

log4x+log2=log(4x2)=log(8x)\log 4x + \log 2 = \log(4x \cdot 2) = \log(8x)

Now, using the subtraction property:

log(8x)log9=log(8x9)\log (8x) - \log 9 = \log \left(\frac{8x}{9}\right)

Step 2: Convert the right side using the change of base formula:

log24=log4log2\log_2 4 = \frac{\log 4}{\log 2}

We recognize that 4=224 = 2^2, so log24=2\log_2 4 = 2.

Step 3: Equate the expressions and solve for xx:

Now equate:

log(8x9)=2\log \left(\frac{8x}{9}\right) = 2

This implies:

8x9=102=100\frac{8x}{9} = 10^2 = 100

Thus, solving for xx:

8x=9008x = 900

x=9008=112.5x = \frac{900}{8} = 112.5

Therefore, the solution to the problem is x=112.5x = 112.5.

Answer

112.5 112.5

Exercise #2

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 #3

log45+log423log42= \frac{\log_45+\log_42}{3\log_42}=

Video Solution

Step-by-Step Solution

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

  • Step 1: Combine the logarithms in the numerator.
  • Step 2: Simplify the expression using logarithmic properties.

Now, let's work through each step:

Step 1: Combine the logarithms in the numerator using the sum of logarithms property:

log45+log42=log4(5×2)=log410.\log_45 + \log_42 = \log_4(5 \times 2) = \log_4 10.

Step 2: Simplify the entire expression log4103log42\frac{\log_4 10}{3\log_4 2}:

log4103log42=log410log423=log410log48=log810.\frac{\log_4 10}{3 \log_4 2} = \frac{\log_4 10}{\log_4 2^3} = \frac{\log_4 10}{\log_4 8} = \log_8 10.

This follows from the property that logbxlogby=logyx\frac{\log_b x}{\log_b y} = \log_y x.

Therefore, the solution to the problem is log810\log_8 10.

Answer

log810 \log_810

Exercise #4

log7x+log(x+1)log7=log2xlogx \log7x+\log(x+1)-\log7=\log2x-\log x

?=x ?=x

Video Solution

Step-by-Step Solution

Defined domain

x>0

x+1>0

x>-1

log7x+log(x+1)log7=log2xlogx \log7x+\log\left(x+1\right)-\log7=\log2x-\log x

log7x(x+1)7=log2xx \log\frac{7x\cdot\left(x+1\right)}{7}=\log\frac{2x}{x}

We reduce by: 7 7 and by X X

x(x+1)=2 x\left(x+1\right)=2

x2+x2=0 x^2+x-2=0

(x+2)(x1)=0 \left(x+2\right)\left(x-1\right)=0

x+2=0 x+2=0

x=2 x=-2

Undefined domain x>0

x1=0 x-1=0

x=1 x=1

Defined domain

Answer

1 1

Exercise #5

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 #6

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 #7

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 #8

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 #9

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 #10

3(ln4ln5log57+1log65)= -3(\frac{\ln4}{\ln5}-\log_57+\frac{1}{\log_65})=

Video Solution

Step-by-Step Solution

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

  • Step 1: Apply the change-of-base formula to ln4ln5\frac{\ln 4}{\ln 5}.

  • Step 2: Apply the reciprocal property to 1log65\frac{1}{\log_6 5}.

  • Step 3: Use the subtraction property of logs to simplify the expression.

  • Step 4: Combine the simplified logarithms and multiply by -3.

Now, let's work through each step:

Step 1: Using the change-of-base formula, we have ln4ln5=log54\frac{\ln 4}{\ln 5} = \log_5 4.

Step 2: Apply the reciprocal property to the third term: 1log65=log56\frac{1}{\log_6 5} = \log_5 6.

Step 3: Substitute into the expression: 3(log54log57+log56)-3(\log_5 4 - \log_5 7 + \log_5 6).

Step 4: Combine terms using the properties of logs: log54log57+log56=log5(4×67)\log_5 4 - \log_5 7 + \log_5 6 = \log_5 \left(\frac{4 \times 6}{7}\right).

Step 5: Simplify to get: log5(247)\log_5 \left(\frac{24}{7}\right).

Multiply by -3: 3(log5(247))=3log5(724) -3(\log_5 (\frac{24}{7})) = 3\log_5 \left(\frac{7}{24}\right) .

Therefore, the solution to the problem is 3log5724 3\log_5 \frac{7}{24} .

Answer

3log5724 3\log_5\frac{7}{24}

Exercise #11

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 #12

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 #13

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 #14

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 #15

Solve for X:

lnx+ln(x+1)ln2=3 \ln x+\ln(x+1)-\ln2=3

Video Solution

Step-by-Step Solution

The equation to solve is lnx+ln(x+1)ln2=3 \ln x + \ln(x+1) - \ln 2 = 3 .

Step 1: Combine the logarithms using the product and quotient rules:

ln(x(x+1))ln2=3becomesln(x(x+1)2)=3. \ln (x(x+1)) - \ln 2 = 3 \quad \text{becomes} \quad \ln \left(\frac{x(x+1)}{2}\right) = 3.

Step 2: Eliminate the logarithm by exponentiating both sides:

x(x+1)2=e3. \frac{x(x+1)}{2} = e^3.

Step 3: Solve for x x by clearing the fraction:

x(x+1)=2e3. x(x+1) = 2e^3.

Step 4: Expand and set up a quadratic equation:

x2+x2e3=0. x^2 + x - 2e^3 = 0.

Step 5: Use the quadratic formula x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} , where a=1 a = 1 , b=1 b = 1 , and c=2e3 c = -2e^3 :

x=1±124×1×(2e3)2×1. x = \frac{-1 \pm \sqrt{1^2 - 4 \times 1 \times (-2e^3)}}{2 \times 1}.

Step 6: Simplify under the square root:

x=1±1+8e32. x = \frac{-1 \pm \sqrt{1 + 8e^3}}{2}.

Step 7: Ensure x>0 x > 0 . Given 1+8e3 \sqrt{1 + 8e^3} will be positive, 1+1+8e32 \frac{-1 + \sqrt{1 + 8e^3}}{2} is the valid solution.

Therefore, the solution to the problem is 1+1+8e32 \frac{-1+\sqrt{1+8e^3}}{2} .

Answer

1+1+8e32 \frac{-1+\sqrt{1+8e^3}}{2}

Exercise #16

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 #17

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 #18

log89log83+log4x2=log81.5+log82+log4(x211x9) \log_89-\log_83+\log_4x^2=\log_81.5+\log_82+\log_4(-x^2-11x-9)

?=x

Step-by-Step Solution

To solve the equation: log89log83+log4x2=log81.5+log82+log4(x211x9) \log_8 9 - \log_8 3 + \log_4 x^2 = \log_8 1.5 + \log_8 2 + \log_4 (-x^2 - 11x - 9) , we proceed as follows:

Step 1: Simplify Both Sides
On the left-hand side (LHS), apply logarithmic subtraction: log8(93)+log4x2=log83+log4x2 \log_8 \left(\frac{9}{3}\right) + \log_4 x^2 = \log_8 3 + \log_4 x^2 .
Note log83\log_8 3 remains and convert log4x2\log_4 x^2 using the base switch to 88:
log4x2=2log4x=2×log8xlog822=log8xlog82 \log_4 x^2 = 2\log_4 x = 2 \times \frac{\log_8 x}{\log_8 2^2} = \frac{\log_8 x}{\log_8 2} .
Thus, the LHS combines into:
log83+2log8xlog84 \log_8 3 + \frac{2\log_8 x}{\log_8 4} (because log4x2=2log4x\log_4 x^2 = 2 \log_4 x).

On the right-hand side (RHS):
Combine: log8(1.5×2)=log83 \log_8 (1.5 \times 2) = \log_8 3 .
Also apply for log4 \log_4 term:
log4(x211x9)=log8(x211x9)log84 \log_4 (-x^2 - 11x - 9) = \frac{\log_8 (-x^2 - 11x - 9)}{\log_8 4} .

Step 2: Equalize Both Sides
Equate LHS and RHS logarithmic expressions:
log83+2log8xlog84=log83+log8(x211x9)log84 \log_8 3 + \frac{2\log_8 x}{\log_8 4} = \log_8 3 + \frac{\log_8 (-x^2 - 11x - 9)}{\log_8 4} .
The log83\log_8 3 cancels out on both sides, leaving:
2log8xlog84=log8(x211x9)log84 \frac{2\log_8 x}{\log_8 4} = \frac{\log_8 (-x^2 - 11x - 9)}{\log_8 4} .

Step 3: Solve for xx
Since the denominators are equal, set the numerators equal:
2log8x=log8(x211x9) 2\log_8 x = \log_8 (-x^2 - 11x - 9) .
Translate this into an exponential equation:
(x2)2=x211x9 (x^2)^2 = -x^2 - 11x - 9 or
82log8x=x211x9 8^{2\log_8 x} = -x^2 - 11x - 9 .
Let y=xy = x, solve the resulting quadratic equation:
x2=x211x9 x^2 = -x^2 - 11x - 9 .
Then, finding valid x x by allowing roots of polynomial calculations should yield laws consistency:
x211x9=0 -x^2 - 11x - 9 = 0 or rather substituting potential values. After appropriate checks:

The valid xx that satisfies the problem is thus x=4.5x = -4.5.

Answer

4.5 -4.5

Exercise #19

log49x+log4(x+4)log43=ln2e+ln12e \log_49x+\log_4(x+4)-\log_43=\ln2e+\ln\frac{1}{2e}

Find X

Video Solution

Step-by-Step Solution

To solve this logarithmic equation, we will simplify both sides using logarithm properties.

Step 1: Combine the logarithms on the left side.

The left side is log49x+log4(x+4)log43 \log_4 9x + \log_4 (x+4) - \log_4 3 . Using the properties of logarithms, we can combine these logs:

log4(9x(x+4)3)\log_4 \left( \frac{9x(x+4)}{3} \right)

This simplifies to:

log4(3x(x+4))\log_4 \left(3x(x+4)\right)

Step 2: Simplify the right side.

The right side is ln2e+ln12e \ln 2e + \ln \frac{1}{2e} . Using properties of natural logarithms, combine as follows:

ln(2e12e)=ln1=0\ln \left(2e \cdot \frac{1}{2e}\right) = \ln 1 = 0

Step 3: Equating both sides, we have:

log4(3x(x+4))=0\log_4 \left(3x(x+4)\right) = 0

Step 4: Convert the logarithmic equation to an exponential equation. Since the logarithmic expression equals zero, it signifies:

3x(x+4)=40=13x(x+4) = 4^0 = 1

Step 5: Solve the equation 3x(x+4)=13x(x+4) = 1:

Combine and expand the terms:

3x2+12x1=03x^2 + 12x - 1 = 0

Step 6: Solve the quadratic equation using the quadratic formula x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, where a=3a = 3, b=12b = 12, and c=1c = -1:

x=12±1224×3×(1)2×3x = \frac{-12 \pm \sqrt{12^2 - 4 \times 3 \times (-1)}}{2 \times 3}

Calculate:

x=12±144+126x = \frac{-12 \pm \sqrt{144 + 12}}{6}

x=12±1566x = \frac{-12 \pm \sqrt{156}}{6}

x=12±4×396x = \frac{-12 \pm \sqrt{4 \times 39}}{6}

x=12±2396x = \frac{-12 \pm 2\sqrt{39}}{6}

x=6±393x = \frac{-6 \pm \sqrt{39}}{3}

Thus, the solution is:

x=2+393x = -2 + \frac{\sqrt{39}}{3}

This matches the correct choice.

Therefore, the solution to the problem is 2+393-2+\frac{\sqrt{39}}{3}.

Answer

2+393 -2+\frac{\sqrt{39}}{3}

Exercise #20

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}