(c)
f is said to have an extreme value in I if there exists a point c in I such that
f (c) is either a maximum value or a minimum value of f  in I The number  f (c), in this case, is called an extreme value of  f  in I and the point c
is called an extreme point Remark In Fig 6 7(a), (b) and (c), we have exhibited that graphs of certain particular
functions  help us to find maximum value and minimum value at a point