\begin{aligned} J&=\frac{1}{2}\int_{0}^{\infty}-\frac{d}{dt}{x}^{T}P{x}{\rm d}t \\ &=-\frac{1}{2}[{x}^{T}P{x}|_{t=\infty} - {x}^{T}P{x}|_{t=0} ]\\ &=-\frac{1}{2}[0 - {x}^{T}(0)P{x}(0)] \\ &=\frac{1}{2}{x}^{T}(0)P{x}(0) \end{aligned}
說明:1 公式需包含在\begin{aligned}和\end{aligned}中
2. 以等號對其,等號前加&
3. 換行用\\即可