Monday, July 27, 2015

Find x if x^(1+log3 x)=9x^2 .

We'll take logarithms both
sides:


log3 [x^(1+log3 x)] = log3
(9x^2)


We'll apply the power rule to the left
side:


(1+log3 x)*(log3 x) = log3
(9x^2)


We'll apply the product rule to the right
side:


(1+log3 x)*(log3 x) = log3 9 + log3
(x^2)


We'll remove the
brackets:


log3 x + (log3 x)^2 = 2 + 2log3
x


We'll move all terms to one
side:


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


We'll combine like
terms:


(log3 x)^2 - log3 x - 2 =
0


We'll note log3 x = t


t^2 -
t - 2 = 0


We'll apply quadratic
formula:


t1 = [1 + sqrt(1 +
8)]/2


t1 = (1 + 3)/2


t1 =
2


t2 = -1


log3 x =
t1


log3 x = 2


x =
3^2


x1 = 9


log3 x =
t2


log3 x = -1


x2 =
3^-1


x2 =
1/3


The solutions are: {1/3 ;
9}.

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