答案1
\documentclass{article}
\usepackage{lmodern}
\usepackage{amsmath}
\begin{document}
\begin{align*}
u(x,t)&=\begin{cases}
\left\{\frac{2c}{a}\sin^2\left[\frac{\sqrt{a}}{2}(x-ct)\right]\right\}^{1/n}, & |x-ct|\leq\frac{\pi}{\mu},\\
0 & \text{otherwise}
\end{cases}\\
u(x,t)&=\begin{cases}
\left\{\frac{2c}{a}\cos^2\left[\frac{\sqrt{a}}{2}(x-ct)\right]\right\}^{1/n}, & |x-ct|\leq\frac{\pi}{2\mu},\\
0 & \text{otherwise}
\end{cases}
\end{align*}
\end{document}