求sin50°cos70°+sin40°sin70°的值.
问题描述:
求sin50°cos70°+sin40°sin70°的值.
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