Suppose that aₖ ≥ 0, bₖ ≥ 0 for all k ≥ 1. Prove that if ∑[infinity]ₖ₌₁ aₖ and ∑[infinity]ₖ₌₁ bₖ converge, then ∑[infinity]ₖ₌₁ aₖbₖ also converges.