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 Infact, through
graphs, we can even find maximum/minimum value of a function at a point at which it
is not even differentiable (Example 15)