someone asked this exact question earlier, heres what I told them:
Check corollary 6.16:
The Comparison Test
Let asubn and bsubn be a sequence of positive real numbers.suppose that there exists a positive real number K such that
limit when n goes to infinity from asubn/bsubn =K
Prove that sum from n=1 to infinity from asubn converges iff sum from n=1 to infinity from bsubn converges.