Friday, November 12, 2010

Solve for x the equation log2(x)=log2(4)+3logx(2)

We'll write log2 (4) = log2
(2^2)


We'll apply the power
property:


log2 (2^2) = 2*log2
(2)


But log2 (2) = 1 => log2 (4) =
2


We'll write log(x) 8 = 1/log (8)
x


log(2) x =log(8) x*log(2)
8


log(2) 8= log(2) (2^3)


We'll
use the power property of logarithms:


log(2) (2^3) =
3log(2) (2) = 3


log(2) x =3*log(8) x => log(8)
x=log(2) x/3


The equation will
become:


log(2) x - 2 - 3/log(2) x =
0


[log(2) x]^2 - 2log(2) x - 3 =
0


Let log(2) x be t:


t^2 - 2t
- 3 = 0


t1 = [2+sqrt(4 +
12)]/2


t1 = (2+4)/2


t1 =
3


t2 = -1


log(2) x = 3
=> x = 2^3 => x = 8


log(2) x = -1 => x
= 2^-1 => x = 1/2


The requested
solutions of the equation are: x = 1/2 and x = 8.

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