Question

Вычислить cos75-cos15

Answer 1

$\displaystyle cos 75-cos15=-2sin( \frac{75+15}{2})*sin( \frac{75-15}{2})=\\\\=-2sin45*sin30=-2* \frac{ \sqrt{2}}{2}* \frac{1}{2}=- \frac{ \sqrt{2}}{2}$