MathJax测试

$$
\begin{align}
\begin{cases}
I & =\frac{gr^2}{2ha_1} =3.674\times 10^{-3}\ kg\ m^2 \\
M_\mu & =-\frac{2hIb_1}{r} =4.984\times 10^{-4}\ kg\ m^2\ s^{-2}
\end{cases}
\end{align}
$$