Logarithm identity

Algebra Level 3

2 + log 2 3 1 + log 2 3 + 3 + log 3 4 1 + log 3 2 = ? \large\dfrac{2+\log_23}{1+\log_23}+\dfrac{3+\log_34}{1+\log_32} = \ ?


This is a part of the Set .


The answer is 4.000.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

6 solutions

2 + log 2 3 1 + log 2 3 + 3 + log 3 4 1 + log 3 2 = 2 + log 3 log 2 1 + log 3 log 2 + 3 + 2 log 2 log 3 1 + log 2 log 3 = 2 log 2 + log 3 log 2 + log 3 + 3 log 3 + 2 log 2 log 3 + log 2 = 4 log 2 + 4 log 3 log 2 + log 3 = 4 \begin{aligned} \frac{2+\log_2{3}}{1+\log_2{3}} + \frac{3+\log_3{4}} {1+\log_3{2}} & = \frac{2+\frac{\log{3}}{\log{2}}}{1+\frac{\log{3}}{\log{2}}} + \frac{3+\frac{2\log{2}}{\log{3}}}{1+\frac{\log{2}}{\log{3}}} \\ & = \frac{2\log{2} + \log{3}}{\log{2} + \log{3}} + \frac{3\log{3} + 2\log{2}}{\log{3} + \log{2}} \\ & = \frac{4\log{2} + 4\log{3}}{\log{2} + \log{3}} \\ & = \boxed{4} \end{aligned}

Moderator note:

Great! Converting directly to just log 2 , log 3 \log 2, \log 3 makes it easy to see the algebraic manipulation.

2 + log 2 3 1 + log 2 3 + 3 + log 3 4 1 + log 3 2 = log 2 4 + log 2 3 log 2 2 + log 2 3 + log 3 27 + log 3 4 log 3 3 + log 3 2 = log 2 12 log 2 6 + log 3 ( 27 × 4 ) log 3 6 = log 6 12 + log 6 108 = log 6 ( 27 × 4 × 12 ) = log 6 ( 3 4 2 4 ) = 4 log 6 6 = 4 \frac { 2+\log _{ 2 }{ 3 } }{ 1+\log _{ 2 }{ 3 } } +\frac { 3+\log _{ 3 }{ 4 } }{ 1+\log _{ 3 }{ 2 } } \\ =\frac { \log _{ 2 }{ 4 } +\log _{ 2 }{ 3 } }{ \log _{ 2 }{ 2 } +\log _{ 2 }{ 3 } } +\frac { \log _{ 3 }{ 27 } +\log _{ 3 }{ 4 } }{ \log _{ 3 }{ 3 } +\log _{ 3 }{ 2 } } \\ =\frac { \log _{ 2 }{ 12 } }{ \log _{ 2 }{ 6 } } +\frac { \log _{ 3 }{ (27\times 4) } }{ \log _{ 3 }{ 6 } } \\ =\log _{ 6 }{ 12 } +\log _{ 6 }{ 108 } \\ =\log _{ 6 }{ (27\times 4\times 12) } \\ =\log _{ 6 }{ (3^{ 4 }\cdot { 2 }^{ 4 }) } \\ =4\cdot \log _{ 6 }{ 6 } \\ =4

Answer is 4 4 .

We have:

2 + log 2 3 1 + log 2 3 + 3 + log 3 4 1 + log 3 2 = 2 + log 2 3 1 + log 2 3 + 3 + 2 log 3 2 1 + log 3 2 = 1 + 1 1 + log 2 3 + 2 + 1 1 + log 3 2 = 3 + 1 + log 3 2 + 1 + log 2 3 ( 1 + log 2 3 ) ( 1 + log 3 2 ) = 3 + 2 + log 3 2 + log 2 3 1 + log 2 3 + log 3 2 + log 2 3 log 3 2 = 3 + 2 + log 3 2 + log 2 3 2 + log 2 3 + log 3 2 = 4 \quad\dfrac{2+\log_23}{1+\log_23}+\dfrac{3+\log_34}{1+\log_32}\\ =\dfrac{2+\log_23}{1+\log_23}+\dfrac{3+2\log_32}{1+\log_32}\\ =1+\dfrac{1}{1+\log_23}+2+\dfrac{1}{1+\log_32}\\ =3+\dfrac{1+\log_32+1+\log_23}{(1+\log_23)(1+\log_32)}\\ =3+\dfrac{2+\log_32+\log_23}{1+\log_23+\log_32+\log_23\log_32}\\ =3+\dfrac{2+\log_32+\log_23}{2+\log_23+\log_32}=\boxed{4}

Andriane Casuga
Aug 13, 2015

e simplification can be done in various methods but the best method is to separate it as far as possible - like 2/1+log 2(3) + log 2(3)/1+log 2(3) + .... so on. I've done it in my own method and got it as 1 + log 6(216) = 4

Hadia Qadir
Aug 12, 2015

2 + log 2(3) = log 2(4) + log 2(3) = log 2(12) 1 + log 2(3) = log 2(2) + log 2(3) = log 2(6) 3 + log 3(4) = log 3(27) + log 3(4) = log 3(108) 1 + log 3(2) = log 3(3) + log 3(2) = log 3(6)

Now use the change of base formula.

log 2(12)/log 2(6) = log 6(12) log 3(108)/log 3(6) = log 6(108)

So now the original expression can be written as follows.

log 6(12) + log 6(108) = log 6(1296) = log 6(6^4) = 4

Joshua Uwaifo
Aug 12, 2015

An easy way to simplify the solution is see that if you make log(base 2) of 3 = x then log(base 3) of 2 = 1 / x and work accordingly. Grace and peace

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...