已知集合 $M=\left\{x \mid x^{2}-3 x-28 \leqslant 0\right\}, N=\left\{x \mid x^{2}-x-6>0\right\}$, 则 $M \cap N$ 为( )
解析 $\because M=\left\{x \mid x^{2}-3 x-28 \leqslant 0\right\}=\{x \mid-4 \leqslant x \leqslant 7\}$, $N=\left\{x \mid x^{2}-x-6>0\right\}=\{x \mid x<-2$ 或 $x>3\}$,

$\therefore M \cap N=\{x \mid-4 \leqslant x<-2$ 或 $3<x \leqslant 7\}$.