Thursday, August 29, 2013

Solve for x the inequality: 81^(x-1) - 9^(x+1) > 0

We'll the base of the 1st term as power of
9:


9^2*(x-1) - 9^(x+1) >
0


We'll shift to the left, the 2nd
term:


9^2*(x-1) >
9^(x+1)


Since the bases are bigger than unit value, the
function is increasing and we'll get:


2*(x-1)>
(x+1)


We'll remove the
brackets:


2x - 2 > x +
1


We'll subtract x both
sides:


2x - x - 2 > 1


x
- 2 > 1


We'll add 2 both
sides:


x > 2 + 1


x
> 3


The range of values of x, for the
inequality to hold, is (3 , +infinite).

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