求值:cos10°cos40°+cos80°cos50°
问题描述:
求值:cos10°cos40°+cos80°cos50°
请写出详细过程
答
cos10°cos40°+cos80°cos50°
=cos10°cos40°+cos(90°-10°)cos(90°-40°)
=cos10°cos40°+sin10°sin40°
=cos(10°-40°)
=cos(-30°)
=√3/2