Find the sum of the series ∑n=0∞(−1)nx2nn!\sum_{n=0}^{\infty} \frac{(-1)^n x^{2n}}{n!}∑n=0∞n!(−1)nx2n.
exe^xex
e−xe^{-x}e−x
ex2e^{x^2}ex2
e−x2e^{-x^2}e−x2