常用幂级数展开

<p>$$\frac{1}{1-x} = \sum_{i=0}x^i$$ <img src="https://www.showdoc.com.cn/server/api/attachment/visitfile/sign/d210a1fa8d10cf400b146e6e740e17d3" alt="" /> <img src="https://www.showdoc.com.cn/server/api/attachment/visitfile/sign/f3a55690c6be23dcc31b0d727b2e4ef2" alt="" /></p>