Base Change of a Logarithm

Logarithms - Reminder

The definition of the log is:
logax=blog_a⁡x=b
X=abX=a^b

Where:
aa is the base of the log
XX is what appears inside the log. It can also appear inside of parentheses
bb is the exponent to which we raise the base of the log in order to obtain the number inside the log.

Base change in logarithm:

Let's switch the positions of the log base and the log content using the following formula:

logax=1logxalog_a⁡x=\frac{1}{log_x⁡a}

Suggested Topics to Practice in Advance

  1. Addition of Logarithms
  2. Power in logarithm

Practice Inverting a Log Function

Examples with solutions for Inverting a Log Function

Exercise #1

1log49= \frac{1}{\log_49}=

Video Solution

Answer

log94 \log_94

Exercise #2

1ln8= \frac{1}{\ln8}=

Video Solution

Answer

log8e \log_8e

Exercise #3

(log7x)1= (\log_7x)^{-1}=

Video Solution

Answer

logx7 \log_x7

Exercise #4

2xlog89log98= \frac{\frac{2x}{\log_89}}{\log_98}=

Video Solution

Answer

2x 2x

Exercise #5

4a2log79 ⁣:log97=16 \frac{4a^2}{\log_79}\colon\log_97=16

Calculate a.

Video Solution

Answer

±2 \pm2

Exercise #6

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

Video Solution

Answer

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

Exercise #7

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

Video Solution

Answer

log411+loge2 \log_411+\log e^2

Exercise #8

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

Video Solution

Answer

7 7

Exercise #9

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

Video Solution

Answer

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

Exercise #10

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

Video Solution

Answer

1 1

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

Answer

12 12

Exercise #12

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

Answer

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

Exercise #13

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

Answer

1.25 1.25

Exercise #14

Find X

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

Video Solution

Answer

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

Topics learned in later sections

  1. Change of Logarithm Base
  2. Logarithms