Clash of logs

Algebra Level 1

l o g 1 0 2 log_{10^2} 1 0 4 10^4 =?


The answer is 2.

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6 solutions

Sandeep Rathod
Dec 6, 2014

l o g 1 0 2 ( 1 0 2 × 1 0 2 ) log_{10^{2}} (10^{2} \times 10^{2})

= l o g 1 0 2 1 0 2 + l o g 1 0 2 1 0 2 = log_{10^{2}} 10^{2} + log_{10^{2}} 10^{2}

= 1 + 1 = 2 = 1 + 1 = 2

Parth Lohomi
Dec 3, 2014

We know that

l o g a b m log_{a^b}m = 1 b \dfrac{1}{b} l o g a m log_{a} m

And

l o g a ( m b ) log_{a}(m^b) = b . l o g a m b. log_{a}m

Using this property

l o g 1 0 2 ( 1 0 4 ) log_{10^2}(10^4) = 2 2 \dfrac{2}{2} l o g 10 10 log_{10}10 = 2 \boxed{2}

What I do when answering logarithms such as log a b \log_{a}b is to ask myself: What will I raise to a a to get b b ? In this case, ( 1 0 2 ) x = 1 0 4 (10^2)^x = 10^4 ( 1 0 2 ) x = ( 1 0 2 ) 2 (10^2)^x=(10^2)^2 x = 2 x=2

Nikhil Raj
May 31, 2017

l o g 1 0 2 1 0 4 = 1 2 l o g 10 1 0 4 = 4 × 1 2 l o g 10 10 = 2 × 1 = 2 log_{10^2}10^4 = \dfrac{1}{2}log_{10}10^4 = 4 \times \dfrac{1}{2} log_{10}10 = 2 \times 1 = \color{#D61F06}{\boxed2}

l o g a n log_{a^n} b^m)=[m/n][\(log_{a} (b)

Kamal Kaur
Dec 13, 2014

(log 10^4) / (log 10^2) =(4 (log10)) / (2 (log10)) [its log rule that power always comes before log. e.g. log 10^4 = 4*log10] Now, log 10 gets divided by log 10. And 4/2= 2.

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