求sin50°cos70°+sin40°sin70°的值.

分类: 作业答案 • 2022-07-05 15:18:27

问题描述：

答

=cos40cos70+sin40sin70=cos(40-70)=cos(-30)=cos30=二分之根号三

答

sin(A+B)=sinAcosB+cosAsinB
sin50°cos70°+sin40°sin70°
=sin50°cos70°+cos50°sin70°
=sin(50°+70°)
=sin120°
=√3/2

答

利用诱导公式,和sin(A+B)=sinAcosB+cosAsinB
sin50°cos70°+sin40°sin70°
=sin50°cos70°+cos50°sin70°
=sin(50°+70°)
=sin120°
=√3/2

答

sin50°cos70°+sin40°sin70°
=cos40°cos70°+sin40°sin70°
=cos(70°-40°)
=cos30°
=√3/2