the Absoulute max and min f(x)=x^4 -2x^2 +3 on [-2,3] is at x=?

I do not know how to do this.

here are my thoughts.

1) take derivative of f(x) and set equal to 0

f'(x)= 4x^3 -4x = 0

4x(4x^2-1) =0

x=0

x= +1/2

x= -1/2

f(0) = 3

f(1/2) = 2.54 ???

I am confused