The series is divergent for

or

from the ratio test, because the limit ends up greater than 1, there is no need to check them.

The only values you will have to check are the values such that the limit actually equals 1, since that is when the ratio test is inconclusive. So to check the convergence that the endpoints

, substitute these values in and use a different test on each of the resulting series.

Having said that, in this question you don't need to check them, because you are only asked for the RADIUS of convergence. You have already found that it is

.