sin330° = sin(360° - 30°) = sin(-30°) = -sin30° = -1/2
cos240° = cos(180° + 60°) = -cos60° = -1/2
sin225° = sin(180° + 45°) = -sin45° = -√2/2
sin135° = sin(180° - 45°) = sin45° = √2/2
Тогда получаем:
sin330°·sin240° - sin225°·sin135° = -1/2·(-1/2) - (-√2/2)·√2/2 = 1/4 + 1/2 = 3/4
ответ: 3/4.
