Question

求cos15°*cos225°的绝对值-sin315°*cos105°的绝对值的值是多少

Answer 1

原式=|cos15°cos(180°+45°)|-|sin(315°-360°)cos(90°+15°)|=|cos15°(-cos45°)|-|sin(-45°)(-sin15°)|=cos15°cos45°-sin15°sin45°=cos(15°+45°)=cos60°=1/2