Question

Найдите cosb, если sinb= -1/2 и 180*

Answer 1

$cosb= -\sqrt{1-sin^2b}=- \sqrt{1-(- \frac{1}{2} )^2} =- \sqrt{1- \frac{1}{4} } = -\sqrt{ \frac{4}{4} - \frac{1}{4} } =- \sqrt{ \frac{3}{4} } = -\frac{ \sqrt{3} }{2}$