Assume that the series $\displaystyle\sum_{n=1}^{+\infty} a_n x^n$ is convergent when $x=-3$, and it is divergent when $x=20$
Is the series $\displaystyle\sum_{n=1}^{+\infty} a_n (-2)^n$ divergent?
Is the series $\displaystyle\sum_{n=1}^{+\infty} a_n 24^n$ convergent?
I figure I could use a comparison test for the second one, but the first one isn't positive, so I'm not sure.