sin15°*cos165°= 求解答

问题描述:

sin15°*cos165°= 求解答

sin15°*cos165°
=sin15°*cos(180°-15°)
=sin15°*(cos180°cos15°-sin180°sin15°)
=sin15°(-cos15°-0)
=-sin15°cos15°
=(-1/2)sin30°
=-1/2*(1/2)
=-1/4