The Easy Factlog

Algebra Level 2

1 log 2 n + 1 log 3 n + + 1 log 2006 n \large\dfrac { 1 }{ \log _{ 2 }{ n } } +\dfrac { 1 }{ \log _{ 3 }{ n } } +\ldots +\dfrac { 1 }{ \log _{ 2006 }{ n } }

If n = 2006 ! n=2006! , then what is the value of the expression above?

0 2006! 1 2006

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3 solutions

Rohit Sachdeva
Sep 24, 2014

l o g a b = 1 / l o g b a log_{a}b =1/ log_{b}a

Hence the given expression becomes:

l o g n 2 + l o g n 3 + . . . . . . l o g n 2006 log_{n}2+log_{n}3+......log_{n}2006

= l o g n ( 2.3.4....2006 ) = log_{n}(2.3.4....2006)

= l o g n n = 1 =log_{n}n = 1

marvelous !!!!

Zack Yeung - 6 years, 1 month ago
Vishal S
Jan 2, 2015

1/log(n,2)+1/log(n.3)+..........+1/log(n,2006) =>log(2,n)+log(3,n)+......log(2006,n)

=>log((2 x 3 x 4 x.....x 2006),n) =log(2006!,n)

Given that n=2006!

by substituting n value as 2006! in log(2006!,n)

We get log(2006!,1)=log(2006!,2006!)=1

therefore 1/log(n,2)+1/log(n.3)+..........+1/log(n,2006) when n=2006! is 1

U Z
Sep 20, 2014

its a property that 1/log to the base a of b is equal to log to the base b of a thus solving we get log to the base n of n that is equal to 1

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