How can i prove these two convergence theorem?

[darthprince]

1. If {an} and {bn} are convergent, then {an士bn} and {anbn} are also convergent

2. If {an} and {bn} are convergent and there exists a constant k>0 such that |bn| > k for all n=1, 2, ..., then {an/bn} is also convergen

 

[CompuChip]

Well, given that an converges to a and bn converges to b, you could "guess" the limits of the other series and then try to prove that they actually are the limits from the definition.

E.g. you can try to show that
\forall_{\epsilon > 0} \exists_{N_+} : n > N_+ \implies |(a_n + b_n) - L| < \epsilon
where L = a + b is the postulated limit. Of course you already know that given such an \epsilon you can find N_a and N_b such that
n > N_a \implies |a_n - a| < \epsilon
and
n > N_b \implies |b_n - b| < \epsilon