Question

5. Вычислите
cos 107° cos17° - sin107°sin17°

Answer 1

Ответ:

cos 107° cos17° - sin107°sin17°=cos 107° cos17° - (sin 90°cos17° + cos90°sin17°)=cos 107° cos17° - (0*cos17° + 1*sin17°)=cos 107° cos17° - sin17°=cos(107°-17°)=cos 90°=0

Тождество:cos(a-b)=cos(a)cos(b)+sin(a)sin(b)