Kąt α jest ostry oraz sinα= 4/5. Wtedy

$\displaystyle \cos\alpha= \frac{1}{5}$\displaystyle \cos\alpha= \frac{1}{5}

$\displaystyle \cos\alpha= -\frac{1}{5}$\displaystyle \cos\alpha= -\frac{1}{5}

$\displaystyle \cos\alpha= -\frac{3}{5}$\displaystyle \cos\alpha= -\frac{3}{5}

$\displaystyle \cos\alpha= \frac{3}{5}$\displaystyle \cos\alpha= \frac{3}{5}