помогите пожалуйста вычислить: a) cos52° cos68°-sin52° sin68°
b)cos17°-cos43° c)3sin15°-cos15°
b)cos17°-cos43° c)3sin15°-cos15°
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b) cos17°-cos43°= -2 * sin 30° * sin (-13°)= 2 * sin 30° * sin 13°= sin 13°
с) 3sin15°-cos15°= 3 (sin 15° - sin (90°-15°))= 3(sin 15° - sin 75°)=3*2* sin( -30°)* cos45°)=3*2* (-0,5)* (√2/2)= - (3√2) / 2