cos47°cos13°－cos43°sin13°的值
问题描述：
cos47°cos13°－cos43°sin13°的值
答
cos47°cos13°－cos43°sin13°=根号3/2
答
cos47°cos13°－cos43°sin13°
=cos47°cos13°－sin47°sin13°
=cos(47+13)
=cos60°
=1/2;