若最简二次根式 $m \sqrt{2 a+1}$ 满足 $m \sqrt{2 a+1}+\sqrt{7}=0$, , 则 $m^{a}=$
解: $\because$ 最简二次根式 $m \sqrt{2 a+1}$ 满足 $m \sqrt{2 a+1}+\sqrt{7}=0$,

$\therefore m=-1,2 a+1=7$,

$\therefore a=3$,

$\therefore(-1)^{3}=-1$