Tutorial Exercise Find the interval of convergence of the power series. (Be sure to include a check for convergence at the endpoints of the interval.) n = 1/+1 (-9x)-1 Step 1 Recall the Ratio Test which states that, if a is a series with nonzero terms, and lim For any fixed value of x such that x + 0, let a = (-9x)" -1. Then, lim n+1 (n + 1)(-9x) 7+2 = lim 318 an 918 3- n(-9x)" n+1 1 lim 818 (n + 1)(-9x)" 7 +2 (n + 1) n + 1 1, or lim n+1 519 a n n , then a diverges. n