Hello .the question is ,The bending moment,M.at a position x m from the end of a simply supported beam of lenght l m carrying a uniformly distrbuted load

of wkNm-1 is given by

M= w/2 l (l -x)-w/2 (l-x)^2

Show using the above expression, that the maximum bending moment occurs atthe mid point of beam and determines its value interms of w and l

I have not got a clue !