sin163°sin223°+sin253°sin313°的值为( )求详解,

来源:学生作业学帮网 编辑:学帮网 时间:2024/05/28 02:44:42

sin163°sin223°+sin253°sin313°的值为( )求详解,

sin163°sin223°+sin253°sin313°
=sin(180º-17°)sin(180º+43°)+sin(270º-17°)sin(270º+43°)
=-sin17°sin43°+cos17°cos43°
=cos17°cos43°-sin17°sin43°
=cos(17°+43°)
=cos60°
=0.5