15°cos7°-cos11°cos79°=
15°cos7°-cos11°cos79° cos(15°) × cos(7°) = 0,9587259617 cos(11°) × cos(79°) = 0,1873032967 0,9587259617-0,1873032967 0,9587259617 – 0,1873032967 = 0,771422665