Rolle's Theorem is a special case of the Mean Value Theorem which
says that there has to be a point between a and b where the
instantaneous rate of change
is equal to the average rate of change between a and
b. More precisely:
Mean Value Theorem: If f is a
function that is continuous on the closed interval
[a,b] and differentiable on the open
interval (a,b), then there is a point c
between a and b such that f′(c)=f(b)−f(a)b−a.