Taylor series problem

[imath]\sum_{n=0}^\infty \frac{(-x)^{6n+1}}{(2n)!}= -x\sum_{n=0}^\infty\frac{(x)^{6n}}{(2n)!}= -x\sum_{n=0}^\infty\frac{((x)^3)^{2n}}{(2n)!}[/imath].

Now, what is the Taylor's series for cos(x)?
 
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