solve for x^2 [resolved]

[dolor]

I wanna know what x^2 is equal to if
(x+9)^(1/3) - (x-9)^(1/3) = 3

I've got this, but I'm not sure ..someone tell me if I'm using magic anywhere.

[(x + 9)^(1/3)]^3 = [3 + (x - 9)^(1/3)]^3 //cube both sides
x + 9 = 27 + x - 9
(x + 9)^2 = (27 + x - 9)^2 //square both sides
x^2 + 18x + 81 = x^2 + 36x + 324 //the x^2 cancels out

-243 = 18x
x = -243/18 //solve for x

so if you square both sides again...

x^2 = (-243/18)^2