$$y=- \cos (x+ \frac{ 5 \pi }{ 2 } )-7$$
$x=\frac{-2\arccos(y+7)+4\pi n_{1}-3\pi }{2}\text{, }n_{1}\in \mathrm{Z}$
$x=\frac{2\arccos(y+7)+4\pi n_{2}-7\pi }{2}\text{, }n_{2}\in \mathrm{Z}\text{, }y\geq -8\text{ and }y\leq -6$
$y=-\cos(\frac{2x+5\pi }{2})-7$
