Wednesday, February 4, 2015

What is (log3 x)^2=log3 (x^2) + 3 ?

Since we have the term log3 x^2, we'll use the power property of
logarithms:log3 x^2 = 2 log3 x.


The given equation (log3 x)^2 = log3
x^2 + 3 converts to


(log3 x)^2 - 2log3 x - 3 =
0


We'll substitute  log3 x = u.


We'll
re-write the equation:


 u^2 - 2u -3
=0


Factoring, we'll get:


(u-3)(u+1)
=0


We'll put each factor as zero:


u-3 =
0


So, u = 3


u + 1 =
0


u =  -1


But log3 x = 3 => x =
3^3 => x = 27


log3 x = -1
=> x = 3^-1 => x =
1/3


Since both solutions are positive,
we'll accept them.

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