Sin^2 165* - cos^2 165*=

Question

Sin^2 165* - cos^2 165*=

Comments

165=(360-30)/2

Answer 1

Используем формулы sin²α=(1-cos2α)/2  cos²α=(1+cos2α)/2
(1-cos330°)/2-(1+cos330°)/2=-cos330°=-cos(360°-30°)=-cos30°=-√3/2