cos7°=cos(15°-8°)=cos8°cos15°+sin8°sin15°,那么cos7°-cos8°cos15°=sin8°sin15°；cos23°=cos(8°+15°)=cos8°cos15°-sin8°sin15°,那么cos23°-cos8°cos15°=-sin8°sin15°所以原式=(sin8°sin15...