http://www.cnblogs.com/yingzi1028/p/6257011.html //飘雪花
http://www.cnblogs.com/yingzi1028/p/6253718.html //右侧打赏
http://www.cnblogs.com/ryantu/p/3285057.html//数学公式 eg: x=frac{{-b}pmsqrt{b^2-4ac}}{2a}
$x=frac{{-b}pmsqrt{b^2-4ac}}{2a}$