9^x - 4 X 3^x = 45. Find x
In words:
9 raised to the power x minus 4 multiplied by 3 raised to the power x is equal to 45. Find x.
or
(3^x)^2 - 4(3x) -45 = 0
let 3^x = y
y2 - 4y - 45 = 0
(y-9)(y+5) = 0
y = 9 or y = -5
3^x = 9
x = 2
or
3^x = -5, which has no solution.
so x = 2