sin65°sin5°+sin25°sin85°=?

来源:学生作业帮助网 编辑:六六作业网 时间:2024/12/28 19:11:08
sin65°sin5°+sin25°sin85°=?sin65°sin5°+sin25°sin85°=?sin65°sin5°+sin25°sin85°=?sin65°sin5°+sin25°sin8

sin65°sin5°+sin25°sin85°=?
sin65°sin5°+sin25°sin85°=?

sin65°sin5°+sin25°sin85°=?
sin65°sin5°+sin25°sin85°
=sin65sin5+cos65cos5
=cos(65-5)
=cos60
=1/2

sin65°sin5°+sin25°sin85°
=sin65°sin5°+cos65°cos5°
=cos(65°-5°)
=cos60°
=1/2

原式=cos25°sin5°+sin25°cos5°
=sin(5°+25°)
=sin30°
=1/2