幂级数∑n=1∞[2n/(n+1)]xn的收敛半径R=_____.

幂级数∑n=1[2n/(n+1)]xn的收敛半径R=_____.
【正确答案】:1/2。解析:limn→∞[2n+1(n+2)]/[2n/(n+1)]=2limn→∞[(n+1)/(n+2)]=2,所以R=1/2.