# extremum

An extremum is a point on a curve *f (x)* at which
there is an instantaneous change of sign of the derivative *f '(x)*.
If *f '(x)* is defined at this point it has value 0. There are two
types of extrema: maximum and minimum. At a **maximum** *f
'(x)* changes from positive to negative; at a **minimum** *f '(x)* changes from negative to positive. Points of inflection are not extrema.