# Math Help - Infinite Series with Double Alternating Signs

1. ## Infinite Series with Double Alternating Signs

What is an example of an infinite series that has double alternating signs?? --++--++ or ++--++--

Something like: (-1)^(an expression of K)

$\sum_{k=0}^{\infty}\sin\left((2k+1)\,\frac{\pi}{4} \right)\,\frac{1}{x^{k}}?$