已知sinx+siny=0.4,cosx+cosy=1.2,则cos(x-y)=______.
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已知sinx+siny=0.4,cosx+cosy=1.2,则cos(x-y)=______.
![已知sinx+siny=0.4,cosx+cosy=1.2,则cos(x-y)=______.](/uploads/image/z/14979904-16-4.jpg?t=%E5%B7%B2%E7%9F%A5sinx%2Bsiny%3D0.4%EF%BC%8Ccosx%2Bcosy%3D1.2%EF%BC%8C%E5%88%99cos%EF%BC%88x-y%EF%BC%89%3D______%EF%BC%8E)
∵sinx+siny=0.4,①
cosx+cosy=1.2,②
①2+②2得:2+2sinxsiny+2cosxcosy=1.6,
∴cos(x-y)=-
1
5,
故答案为:-
1
5.
cosx+cosy=1.2,②
①2+②2得:2+2sinxsiny+2cosxcosy=1.6,
∴cos(x-y)=-
1
5,
故答案为:-
1
5.
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