In h(x) = f(x) + f(-x), then h (x) has got an extreme value at a point where f'(x) is
even function.
odd function.
zero
None of these
We have, h'(x) = f'(x) - f'(-x) For extreme value of h(x), h'(x) = 0 ⇒ f'(x) = f'(-x) ⇒ f'(x) is an even function.