Hi im having trouble understanding part of the power series. Im trying to find the radius of convergence using the ratio test, the initial problem is the sum of k=1 as k goes to infinity of x^k/(1+k^2). When i use the ratio test i get it down to xk^2/(k+1)^2, now my book goes from this to just the absolute value of x. If you expand (k+1)^2 the k^2's cancel but what happens to the 2k+1 are you allowed to just drop it or am i missing something?

Thanks for the help.