$\displaystyle \cos\alpha= \frac{1}{2}$\displaystyle \cos\alpha= \frac{1}{2}

$\displaystyle \cos\alpha= \frac{\sqrt{2}}{2}$\displaystyle \cos\alpha= \frac{\sqrt{2}}{2}

$\displaystyle \cos\alpha= \frac{\sqrt{3}}{2}$\displaystyle \cos\alpha= \frac{\sqrt{3}}{2}

$\cos\alpha=1$\cos\alpha=1