Wednesday, September 24, 2014

(log 2 x^2)^2 + log 2 x -18 = 0

The equation `(log_2 x^2)^2 + log_2 x -18 = 0` has to be
solved


`(log_2 x^2)^2 + log_2 x -18 =
0`


Use the property of logarithm, log a^b = b*log a. This
gives:


`(2*log_2 x)^2 + log_2 x -18 =
0`


Now take the square of the first
term


`2^2*(log _2x)^2 + log_2 x -18 =
0`


Let `y = log_ 2x`


4y^2 + y
- 18 = 0


4y^2 + 9y - 8y - 18 =
0


y(4y + 9) - 2(4y + 9) = 0


(y
- 2)(4y + 9) = 0


y = 2 and y =
-9/4


Now `y = log_2 x`


`log_2
x = 2`


x = 2^2 = 4


`log_2 x =
-9/4`


x = 2^(-9/4) which is approximately
0.21022


The solution of the equation is x = 4 and x =
0.21022

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