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