幂级数∑n=1∞[(-1)n(1/2n)xn+3nxn]的收敛半径是()

幂级数∑n=1[(-1)n(1/2n)xn+3nxn]的收敛半径是()
A、R=1/3
B、R=1/2
C、R=2
D、R=3
【正确答案】:A