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 Therefore, by first derivative test, x = – 1 is a point of local maxima
and local maximum value is  f (–1) = 5 Values of  x
Sign of f ′′′′′(x) = 3(x – 1) (x + 1)
Close to 1     
to the right (say 1