# Math Help - Summation notation of a Taylor seires

1. ## Summation notation of a Taylor seires

I have expanded the taylor series of sin(x) about pi/4 and I am trying to write it in summation notation. However, i can't figure out the expression for the sign of each term. The sign of the terms are ++--++--++--.... i can't figure out how to write this as (-1)^power so that it forms this pattern.

2. Originally Posted by beachbump
I have expanded the taylor series of sin(x) about pi/4 and I am trying to write it in summation notation. However, i can't figure out the expression for the sign of each term. The sign of the terms are ++--++--++--.... i can't figure out how to write this as (-1)^power so that it forms this pattern.
$\displaystyle \sum\limits_{n = 0}^\infty {\left( { - 1} \right)^{\left\lfloor {\frac{n}{2}} \right\rfloor } a_n }$
That gives $++--++--\cdots$

You may have to adjust the index and/or exponent.