# Thread:

1. ## Inverse Function

Is the inverse of f(x) = 9-2x^2
f-1(x) = -sqrt( (9/2) - (x/2) )

Thanks,
D.

2. Originally Posted by dboyd435
Is the inverse of f(x) = 9-2x^2
f-1(x) = -sqrt( (9/2) - (x/2) )

Thanks,
D.
The working in your post is correct except I do not see why you can't have a plus or minus infront of that square root unless there is something about the domain you're not telling me

$y = 9-2x^2$

$2x^2 = 9-y$

$x^2 = \frac{9-y}{2}$

$x = \pm \sqrt{\frac{9-y}{2}}$

$f^{-1}(x) = \pm \sqrt{\frac{9-x}{2}}$

Bear in mind that's not a function since it's not one to one - the domain would have to be restricted to make it a function. t

3. Thanks, ya, I meant to put +/- but i guess it didn't type out for some reason.
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