We know that 1 1 − r = [infinity] n = 0 rn has interval of convergence (−1, 1). This means the series converges for |r| < 1. Therefore, the series f(x) = 1 2 + x = [infinity] n = 0 (−1)n xn 2n + 1 will converge when − x 2 < 1. Thus, what is the interval of convergence for f(x)? (Enter your answer using interval notation.)