[M4.4]
is: a test to determine the location and nature of a local extremum of a given function [M4.4]
involves: (a) finding the points at which 
(b) investigating the behaviour of the sign of 
at those points. If 
and 
there is a local maximum at 
If and 
there is a local minimum at If and 
then further investigation is required. [M4.4]
See stationary points and graph sketching in the Maths handbook.
Copyright 1997, The Open University