$\displaystyle \cos\alpha= \frac{1}{4}$\displaystyle \cos\alpha= \frac{1}{4}

$\displaystyle \cos\alpha= \frac{\sqrt{7}}4{}$\displaystyle \cos\alpha= \frac{\sqrt{7}}4{}

$\displaystyle \cos\alpha= \frac{7}{16}$\displaystyle \cos\alpha= \frac{7}{16}

$\displaystyle \cos\alpha= \frac{\sqrt{13}}{16}$\displaystyle \cos\alpha= \frac{\sqrt{13}}{16}