设cosx-cosy=Z, (sinx+siny)^2=1 , (sinx)^2+(siny)^2+2sinxsiny=1, (cosx-cosy)^2=Z^2, (cosx)^2+(cosy)^2-2cosxcosy=Z^2. 2-2cos(x-y)=1+Z^2. Z^2=1-2cos(x-y)=[0,3], Z=[-根3,根3] cosx-cosy的取值范围 :[-根3,根3]
答：解：：∵（sinx-siny）^2+（cosx+cosy)^2 =（sin^2x+cos^2x）+（sin^2y+cos^2y）+2（cosxcosy-sinx...详情>>
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