Aus Online Mathematik Brückenkurs 2
The function has critical points at the points x=a and x=d, (see figure below), i.e. the derivatives are equal to zero, but note that x=b and x=c are not critical points (the derivative is not even defined at these points).
The function has local minimum points at x=a, x=c and the right endpoint of the interval of definition and the local maximum points at the left endpoint, x=b, and x=d. Of these, x=b is the global maximum and x=a is the global minimum.
Between the local extreme points, the function is strictly increasing or decreasing.
