\[
   p(t)=
   e^{-P(t)}
   \left\{
      \int_{t_0}^t e^{P(\tau)} q(\tau)~dt\tau
      +c
   \right\},
   ~c \in \mathbb R
\]


\[
   f(x)=
   \left\{
      \begin{array}{cc}
        x^2+1, & x<-1\\
        x^2-1, & -1\leq x<1\\
        x^2+1, & x\geq 1\\
      \end{array}
   \right.
\]


