Examples with solutions for Subtraction of Logarithms: Applying the formula

Exercise #1

log53log52= \log_53-\log_52=

Video Solution

Step-by-Step Solution

To solve the problem, we employ the property of logarithms for subtraction:

  • Step 1: Recognize the expression log53log52 \log_5 3 - \log_5 2 .
  • Step 2: Apply the logarithmic property for subtraction, logbalogbc=logb(ac) \log_b a - \log_b c = \log_b \left( \frac{a}{c} \right) .
  • Step 3: Substitute into the property: log53log52=log5(32) \log_5 3 - \log_5 2 = \log_5 \left( \frac{3}{2} \right) .

By applying the property, we simplify the expression to log532 \log_5 \frac{3}{2} . This is equivalent to log51.5 \log_5 1.5 . Therefore:

Therefore, the result of the expression is log51.5 \log_5 1.5 .

Answer

log51.5 \log_51.5

Exercise #2

log29log23= \log_29-\log_23=

Video Solution

Step-by-Step Solution

To solve the problem of evaluating log29log23\log_2 9 - \log_2 3, we apply the properties of logarithms as follows:

  • Step 1: Recognize that the expression uses a subtraction of logarithms with the same base: log29log23\log_2 9 - \log_2 3.
  • Step 2: Use the logarithmic subtraction rule: logbAlogbB=logb(AB)\log_b A - \log_b B = \log_b \left(\frac{A}{B}\right).
  • Step 3: Simplify using this rule: log29log23=log2(93)\log_2 9 - \log_2 3 = \log_2 \left(\frac{9}{3}\right).
  • Step 4: Perform the division: 93=3\frac{9}{3} = 3.
  • Step 5: Therefore, log2(93)=log23\log_2 \left(\frac{9}{3}\right) = \log_2 3.

Thus, the simplified and evaluated result is log23 \log_2 3 .

Answer

log23 \log_23

Exercise #3

log75log72= \log_75-\log_72=

Video Solution

Step-by-Step Solution

To solve the problem, let's use the rules of logarithms:

  • Step 1: Recognize that we are dealing with the subtraction of logarithms sharing the same base, which calls for the identity logbMlogbN=logb(MN)\log_b M - \log_b N = \log_b \left(\frac{M}{N}\right).
  • Step 2: Apply this identity to the expression log75log72\log_7 5 - \log_7 2.
  • Step 3: Realize that this can thus be expressed as a single logarithm: log7(52)\log_7 \left(\frac{5}{2}\right).
  • Step 4: Simplify the fraction, yielding log72.5\log_7 2.5.

Therefore, the simplification results in the expression: log72.5\log_7 2.5.

This matches the correct answer from the given choices.

Answer

log72.5 \log_72.5

Exercise #4

12log39log31.5= \frac{1}{2}\log_39-\log_31.5=

Video Solution

Step-by-Step Solution

To solve the problem 12log39log31.5 \frac{1}{2}\log_39-\log_31.5 , we need to apply the rules of logarithms:

  • **Step 1: Simplify with the power rule**
    Using the power rule 12log39=log391/2 \frac{1}{2}\log_39 = \log_39^{1/2} . Since 9=329 = 3^2, we have 91/2=321/2=319^{1/2} = 3^{2 \cdot 1/2} = 3^1. Thus, 12log39=log33=1\frac{1}{2}\log_39 = \log_3 3 = 1.
  • **Step 2: Apply the subtraction rule**
    Now, the expression becomes 1log31.51 - \log_3 1.5. Using the subtraction rule: 1log31.5=log33log31.5=log3(31.5)1 - \log_3 1.5 = \log_3 3 - \log_3 1.5 = \log_3 \left(\frac{3}{1.5}\right).
  • **Step 3: Simplify the fraction**
    Calculate 31.5\frac{3}{1.5}: it simplifies to 2 because 3÷1.5=23 \div 1.5 = 2.

Thus, the simplified expression is log32\log_3 2.

Using the provided answer choices, the correct answer matches choice log32 \log_3 2 , which corresponds to choice 2.

Therefore, the solution to the problem is log32 \log_3 2 .

Answer

log32 \log_32

Exercise #5

14log61296log612log63= \frac{1}{4}\cdot\log_61296\cdot\log_6\frac{1}{2}-\log_63=

Video Solution

Step-by-Step Solution

We break it down into parts

log61296=x \log_61296=x

6x=1296 6^x=1296

x=4 x=4

144log612log63= \frac{1}{4}\cdot4\cdot\log_6\frac{1}{2}-\log_63=

log612log63= \log_6\frac{1}{2}-\log_63=

log6(12:3)=log616 \log_6\left(\frac{1}{2}:3\right)=\log_6\frac{1}{6}

log616=x \log_6\frac{1}{6}=x

6x=16 6^x=\frac{1}{6}

x=1 x=-1

Answer

1 -1

Exercise #6

15log810242log812= \frac{1}{5}\log_81024-2\log_8\frac{1}{2}=

Video Solution

Answer

log816 \log_816