2.阿贝尔法(构造幂级数法) o ∑an=lim∑qnx”,求得(x)= ∑anx n=0 x→1 =0 ∑an=lim(x).(逐项积分、逐项求导) =0 2n-1 例4求∑ 的和 2 解令(x)=∑ 2n-1、2n2 22.阿贝尔法(构造幂级数法): lim , 0 1 0 n n n x n an a x → = = − = ( ) , 0 n n s x an x = 求得 = lim ( ). 1 0 a s x x n n → − = = (逐项积分、逐项求导) 例4 . 2 2 1 1 求 的和 = − n n n 解 , 2 2 1 ( ) 2 2 1 − = − = n n n x n 令 s x (− 2, 2)