Question

Порівняйте cos 105° і sin 75°​

Answer 1

cos105°-sin75°=cos105°-sin(90°-15°)=cos105°-cos15°=-2sin((105°+15°)/2)sin((105°-15°)/2)=-2sin(120°/2)sin(90°/2)=-2sin60°sin45°=-2*√3/2*√2/2=-3*√2/2=-√6/2.