hello
- a
- f
- v
<script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=default"></script>
$$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$$
\(x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\)
![](http://chart.googleapis.com/chart?cht=tx&chl=\Large x=\frac{-b\pm\sqrt{b^2-4ac}}{2a})
$X_vv$