I don't understand this conversion!(adsbygoogle = window.adsbygoogle || []).push({});

[tex]\sum_{n=1}^\infty \frac{sin(n\pi /2)}{n!} = \sum_{n=0}^\infty \frac{(-1)^n}{(2n+1)!} [/tex]

I know that the numerator of the left side is 0 when n is an even number. When n is odd, the numerator is either +1 or -1. But how do i continue?

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# Homework Help: Series with Factorial

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