sin5°sin25°-sin95°sin65°的值是A,1/2 B,-1/2 C,根号3/2 D,-根号3/2

来源:学生作业帮助网 编辑:六六作业网 时间:2024/12/29 09:56:05
sin5°sin25°-sin95°sin65°的值是A,1/2B,-1/2C,根号3/2D,-根号3/2sin5°sin25°-sin95°sin65°的值是A,1/2B,-1/2C,根号3/2D,

sin5°sin25°-sin95°sin65°的值是A,1/2 B,-1/2 C,根号3/2 D,-根号3/2
sin5°sin25°-sin95°sin65°的值是
A,1/2 B,-1/2 C,根号3/2 D,-根号3/2

sin5°sin25°-sin95°sin65°的值是A,1/2 B,-1/2 C,根号3/2 D,-根号3/2
sin5·×sin25·-sin95·×sin65· =sin5·×cos65·-sin85·×sin65· =sin5·×cos65·-cos5·×sin65· =sin(5·-65·) =sin(-60·) =-sin60· =-√3/2

D
sin5°sin25°-sin95°sin65°=sin5°sin25°-cos5°cos25°=-cos(5°+25°)=-cos30°=-根号3/2

原式=sin5°sin25°-cos5°cos25°=-(cos5°cos25°-sin5°sin25°)
=-cos(5°+25°)=-cos30° 故答案为D