Chapter 1.2, Problem 81E

Proof Prove that if the limit of f(x) as x approaches c exists, then the limit must be unique. [Hint: Let $\underset{x\to 0}{\lim }f(x)=L_1$, and $\underset{x\to 0}{\lim }f(x)=L_2$, and prove that $L_1=L_2$.]