作业帮求sin50°cos70°+sin40°sin70°的值.
来源：学生作业帮助网 编辑：作业帮 时间：2024/05/09 14:28:45
求sin50°cos70°+sin40°sin70°的值.
求sin50°cos70°+sin40°sin70°的值.
求sin50°cos70°+sin40°sin70°的值.
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
sin50°cos70°+sin40°sin70°
=cos40°cos70°+sin40°sin70°
=cos(70°-40°)
=cos30°
=√3/2
sin(A+B)=sinAcosB+cosAsinB
sin50°cos70°+sin40°sin70°
=sin50°cos70°+cos50°sin70°
=sin(50°+70°)
=sin120°
=√3/2
=cos40cos70+sin40sin70=cos(40-70)=cos(-30)=cos30=二分之根号三
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