28. Prove that f x is continuous at x0 if and only if it is sequentially continuous...

28. Prove that f ðxÞ is continuous at x0 if and only if it is sequentially continuous at x0. (Hint: If continuous, consider the definition in conjunction with definition of xn ! x0. Prove the reverse implication by contradiction, if f ðxÞ is not continuous. . . .)