Question

Let f(t)=2t^4-2x^2-9. at what x does f have a local or absolute minimum or maximum?

I think the question is wrong bcus it is impossible to to have 2 unknown to find the relative max or min...right? Sorry if im wrong.
So i change it to f(x)=2x^4-2x^2-9
so for relative max is x = 0 and relative minimum is x= +/- 0.7071. Plz recheck back the answer.

Answer 1

f' = 8x^3 - 4x = 4x(2x^2-1)

you are correct