cos15°-sin15°=?
问题描述：
cos15°-sin15°=?
答
cos15°-sin15°=cos(15°+15°)=cos30°=√3/2
答
cos15°-sin15°=cos(45°-30°)-sin(45°-30°)
=cos45°cos30°+sin45°sin30°-sin45°cos30°+cos45°sin30°
=√2/2*√3/2+√2/2*1/2-√2/2*√3/2+√2/2*1/2=√2/2.
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...