cos15°-sin15°=?
问题描述：
cos15°-sin15°=?
答
cos15°-sin15°= cos(45°- 30°) - sin(45°- 30°)= cos45°cos30°+ sin45°sin30°- sin45°cos30°+ cos45°sin30°= √2/2 * cos30°+ √2/2 * sin30°- √2/2 * cos30°+ √2/2 * sin30°= √2/2 * ( cos30...