Sin113cos323+cos247cos307=

Объясните как решать

По формулам привидения:

sin113°=sin (180°-67°) = sin67°

cos323°=cos (270°+53°) = sin53°

cos247°=cos (180°+67°) = - cos67°

cos307°=cos (360°-53°) = cos53°

sin113° * cos323°+cos247° * cos307°=

=sin67° * sin53°-cos67° * cos53° = - (cos67° * cos53°-sin67° * cos53°) - cos (67°+53°) = - cos120°=-cos (180°-60°) = - (-cos60°) = cos60°=1/2=0,5