A function
has a local maximum at c if there is an open interval I containing c so that for all x in I ,
, then
is called as a local maximum value of
.
A function
has a local minimum at c if there is an open interval I containing c so that for all x in I ,
, then
is called as a local minimum value of
.

Observe the graph of the function :
\Since for all
close to
,
, the function has a local maximum at
.
The local maximum value is
.

Observe the graph of the function :
\Since for all
close to
and
,
and
, the function has a local minimum at
and
.
The local minimum value is
.
.
.