F(x) = x^4 - 18x^2 + 1; [-4,4}

F'(x) = 4x^3 -36x = 0

Critical points x = -3, x=3

x | f(x)= x^4 - 18x^2 + 1

-------------------------

-4 | -31

-3 | -80

3 | -80

4 | -31

I would had said the absolute max is -4 & 4 and min is -3, 3

The book says max = o, min = -3

Where did I go wrong?

f(x) = (1-x)/(x+3); [0,3]

I got .33333 for the max, -.3333 for the min. The book says max is 0 and min is 3. What did I miss?