Find the inverse function, if exists..

hello

am stopped at this problem -_-

let $\displaystyle f(x)=2x^2-8x$ where x>2

Find a formula for the inverse function of it, if exists.

__My solution:__

f`(x)=4x-..... so f is increas..so its 1-1funct..so inverse is exist.

its easy to prove that the inverse function is exist..=)

But the problem is finding the inverse function

ok let $\displaystyle y=2x^2-8x$ ..

how to find the x in terms of y !!

i tried to get the natural logarthmic of both sides but it failed :S

any help?!