Elaborate cos (x2) as a power series.
1
\(1\ +\ \frac{x^4}{2!} \ +\ \frac{x^8}{4!}\ -\ \ \frac{x^{12}}{6!} \ +\ \dots\)
2
\(1\ -\ \frac{x^4}{2!} \ -\ \frac{x^8}{4!}\ -\ \ \frac{x^{12}}{6!} \ +\ \dots\)
3
\(1\ -\ \frac{x^4}{2!} \ +\ \frac{x^8}{4!}\ +\ \ \frac{x^{12}}{6!} \ +\ \dots\)
4
\(1\ -\ \frac{x^4}{2!} \ +\ \frac{x^8}{4!}\ -\ \ \frac{x^{12}}{6!} \ +\ \dots\)