Mathematics

Problem

Which of the following best defines a critical point of a real-valued function

f

? a) A real number

c

where

f'(c)=0

only. b) A real number

c

in the domain of

f

where either

f'(c)=0

f'

does not exist. c) A real number

c

where

f''(c)=0

. d) A real number

c

where

f'(c)

does not exist but

f

is defined and differentiable elsewhere.