Prove that if f(x) is continuous at a and f(a)0 then 1/f(x) is continuous at a.

Problem: 

Prove that if f(x) is continuous at a and f(a)0 then 1/f(x) is continuous at a.

Answer: 

It is true that if f(x) is continuous at a and f(a)0 then 1/f(x) is continuous at a.