The Mean Value Theorem
If ๐ is continuous on [๐, ๐] and differentiable on (๐, ๐), then there exists some ๐ with ๐ < ๐ < ๐ such that
๐โฒ(๐) = [๐(๐) โ ๐(๐)] / (๐ โ ๐)
This means the instantaneous rate of change at ๐ equals the average rate of change of ๐ over [๐, ๐].