sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)的值为( )
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sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)的值为( )
A.
A.
2 |
![sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)的值为( )](/uploads/image/z/19944274-58-4.jpg?t=sin%EF%BC%8865%C2%B0-x%EF%BC%89cos%EF%BC%88x-20%C2%B0%EF%BC%89%2Bcos%EF%BC%8865%C2%B0-x%EF%BC%89cos%EF%BC%88110%C2%B0-x%EF%BC%89%E7%9A%84%E5%80%BC%E4%B8%BA%EF%BC%88%E3%80%80%E3%80%80%EF%BC%89)
解析:原式=sin(65°-x)cos(x-20°)+cos(65°-x)•cos[90°-(x-20°)]
=sin(65°-x)cos(x-20°)+cos(65°-x)sin(x-20°)
=sin[(65°-x)+(x-20°)]=sin45°=
2
2.
故选B
=sin(65°-x)cos(x-20°)+cos(65°-x)sin(x-20°)
=sin[(65°-x)+(x-20°)]=sin45°=
2
2.
故选B
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