Generaly:

Bol. - Weier. theorem says: if f is continuous on [ a, b ] then f( [ a, b ] ) = [ c, d ] segment. Candidates for min and max ( c and d ) are:

1. z = a and z = b ( f( a ) and f( b ) )

2. f is differential in z and f ' ( z ) = 0 ( f( z ) )

3. f is not differential in z