cos40°cos70°+cos30°cos50°求值

分类: 作业答案 • 2022-06-28 12:00:14

问题描述：

答

[sin(10° + 40°) + sin(10° - 40°)]/2 (利用积化和差公式) = 1 + (cos80° - cos20°)/2 + [sin50° + sin(-30°)]/2 (

答

应该是cos40°cos70°+cos20°cos50°
=cos40°cos70°+sin70°sin40°
=cos(70-40)°
=cos30°
=√3/2