(iii)
The test fails if f ′(c) = 0 and f ″(c) = 0 In this case, we go back to the first derivative test and find whether c is a point of
local maxima, local minima or a point of inflexion ANote  As f is twice differentiable at c, we mean
second order derivative of f exists at c Example 19 Find local minimum value of the function f
given by  f (x) = 3 + |x|, x ∈ R