Find the radius of convergence for ∑n=1∞n!2nxn\sum_{n=1}^{\infty} \frac{n!}{2^n}x^n∑n=1∞2nn!xn using the ratio test.
R=0R = 0R=0
R=2R = 2R=2
R=∞R = \inftyR=∞
R=12R = \frac{1}{2}R=21