Limiting a energy term

Question

A famous Einstein's mass energy equivalence equation is $E= \frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$

I need to prove from the above equation is that E = pc. I know that, i will have to limit $m \rightarrow 0$ but failed to do this. Any help?

Answer 1

You need:

$$\vec{p}=\frac{m \vec{v}}{\sqrt{1-\frac{v^2}{c^2}}}$$