$\displaystyle \frac{\alpha}{2} +\gamma-180^\circ$\displaystyle \frac{\alpha}{2} +\gamma-180^\circ

$\displaystyle 180^\circ- \frac{\alpha}{2}-\gamma$\displaystyle 180^\circ- \frac{\alpha}{2}-\gamma

$180^\circ-\alpha-\gamma$180^\circ-\alpha-\gamma

$\alpha+\gamma-180^\circ$\alpha+\gamma-180^\circ