Find the sum of the power series f(x)=∑n=0∞x4n(4n)!f(x) = \sum_{n=0}^{\infty} \frac{x^{4n}}{(4n)!}f(x)=∑n=0∞(4n)!x4n for all real xxx.
cosh(x)+cos(x)2\frac{\cosh(x) + \cos(x)}{2}2cosh(x)+cos(x)
ex+e−x+2cos(x)4\frac{e^x + e^{-x} + 2\cos(x)}{4}4ex+e−x+2cos(x)
sinh(x)+sin(x)2\frac{\sinh(x) + \sin(x)}{2}2sinh(x)+sin(x)
ex+e−x−2cos(x)4\frac{e^x + e^{-x} - 2\cos(x)}{4}4ex+e−x−2cos(x)