Which series represents cos(2x)\cos(2x)cos(2x)?
∑n=0∞(−1)n(2x)2n(2n)!\sum_{n=0}^{\infty} (-1)^n \frac{(2x)^{2n}}{(2n)!}∑n=0∞(−1)n(2n)!(2x)2n
∑n=0∞(−1)n2x2n(2n)!\sum_{n=0}^{\infty} (-1)^n \frac{2x^{2n}}{(2n)!}∑n=0∞(−1)n(2n)!2x2n
∑n=0∞(−1)nx2n(2n)!\sum_{n=0}^{\infty} (-1)^n \frac{x^{2n}}{(2n)!}∑n=0∞(−1)n(2n)!x2n
∑n=0∞(2x)2n(2n)!\sum_{n=0}^{\infty} \frac{(2x)^{2n}}{(2n)!}∑n=0∞(2n)!(2x)2n