Which series represents e−xe^{-x}e−x?
∑n=0∞xnn!\sum_{n=0}^{\infty} \frac{x^n}{n!}∑n=0∞n!xn
∑n=0∞(−1)nxnn!\sum_{n=0}^{\infty} (-1)^n \frac{x^n}{n!}∑n=0∞(−1)nn!xn
∑n=0∞(−1)nx2nn!\sum_{n=0}^{\infty} (-1)^n \frac{x^{2n}}{n!}∑n=0∞(−1)nn!x2n
∑n=0∞(−x)nn\sum_{n=0}^{\infty} \frac{(-x)^n}{n}∑n=0∞n(−x)n