Chapter 1 - Limits and Continuity - 1.1 Limits (An Intuitive Approach) - Exercises Set 1.1 - Page 60: 18

True

$\displaystyle{\lim_{x \to a}}f(x)$ exists when $ \displaystyle{\lim_{x \to a^+}}f(x) = \displaystyle{\lim_{x \to a^-}}f(x)$ Therefore, for $\displaystyle{\lim_{x \to a}}f(x)$ to exist, both $\displaystyle{\lim_{x \to a^+}}f(x)$ and $\displaystyle{\lim_{x \to a^-}}f(x)$ must exist as well.