Let us first examine the point x = 1 Note that for values close to 1 and to the right of 1, f ′(x) > 0 and  for values close
to 1 and to the left of 1, f ′(x) < 0 Therefore, by first derivative test, x  = 1 is a point
of local minima and local minimum value is f (1) = 1 In the case of x = –1, note that
f ′(x) > 0, for values close to and to the left of –1 and f ′(x) < 0, for values close to and
to the right of – 1