当<img src=http://oss.ouchn.cn/ddzx/N601/jiaoyu/jjsx/50459/unit/chapter_two/images/rw/image073.png style=box-sizing: inherit; border-style: none; vertical-align: middle; color: rgb(58, 58, 58); font-family: Microsoft YaHei font-size: medium; white-space: normal; background-color: rgb(255, 255, 255);/>时,函数<img src=http://oss.ouchn.cn/ddzx/N601/jiaoyu/jjsx/50459/unit/chapter_two/images/rw/image111.png style=box-sizing: inherit; border-style: none; vertical-align: middle; color: rgb(58, 58, 58); font-family: Microsoft YaHei font-size: medium; white-space: normal; background-color: rgb(255, 255, 255);/>是无穷小量.