Use the definition of continuity and the properties of limits to show that the function is continuous at the given number a. f(x) = x + 4x4 3 , a = −1 lim x→−1 f(x) = lim x→−1 3 = lim x→−1 x + lim x→−1 x4 3 = −1 + 4 4 3 = f(−1) = Thus, by the definition of continuity, f is continuous at a = −1.