21. Suppose that the functions ƒ and g are defined throughout an open interval containing the point

Chapter3 Additional and Advanced Exercises Ex21
數學系卡安很閒 所以決定拯救沒辦法用slader和chegg的莘莘學子
21. Suppose that the functions ƒ and g are defined throughout an
open interval containing the point x0, that ƒ is differentiable at x0,
that ƒ(x0) = 0, and that g is continuous at x0. Show that the product ƒg is differentiable at x0. This process shows, for example, that although | x | is not differentiable at x = 0, the product x | x | is differentiable at x = 0.