Give examples to show that if $\displaystyle \sum a_k$ and $\displaystyle \sum b_k$ both diverge, then each of the series $\displaystyle \sum (a_k+b_k)$ and $\displaystyle \sum (a_k-b_k)$ may converge or diverge.

I'm not 100% sure how to complete this, though I was advised to use $\displaystyle \sum_{k=1}^{\infty}1$, which is divergent. I'm not quite sure how to use this, though.

I think for the first one, if I have $\displaystyle b_k=-a_k$, then I can show it is convergent since $\displaystyle \sum (a_k+(-a_k))=0$. This could also work for the second one if I just have $\displaystyle b_k=a_k$.

I've probably got better answers than I think I do, but I could use a second opinion in any case.