Hey all

This is my first ever post so here goes!!

REALLY stuck on two types of question about limits of functions.

In both cases a proof from first principle is required. In case one I need to prove that if f(x) tends to 5 as x tends to 1 then (f(x))^2 tends to 25 as x tends to 1.

Secondly in another question, I need to show that 2/3+x tends to 0 as x tends to infinity.

I am really stuck as to how to even start these sorts of questions, any help would really be appreciated.