"Prove that epsilon delta"?? What does that mean? In any case, please show what you have tried. Do you know the "epsilon-delta" definition of "limit"?
You should know that if then .
So in this case, you need to show , or if you like, to show
This particular proof requires some knowledge of the Mean Value Theorem, in other words, that for some
Here our and , so by the Mean Value Theorem
Therefore we should choose .