Объяснение:
cos15⁰cos25⁰ + cos105⁰cos115⁰ = cos10⁰
cos15⁰cos25⁰ + cos(90+15⁰)cos(90+25⁰) = cos15⁰cos25⁰ -sin15°*(-sin(25°)=
cos15⁰cos25⁰ +sin15°sin25°=cos(15°-25°)=cos(-10°)=cos10°
