Suppose that f is an odd function; i.e., f(-x)=-f(x) for all x. Suppose that f'(x) exists. Which of the following must necessarily be equal to f'(-x)?

A) f'(x)

B) -f'(x)

C) 1/(f'(x))

D) -1/(f'(x))

E) None of the above

i know the answer is A), but I don't know how to solve it. please help!