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已知x^2-2xy-3y^2=0,求x^2+xy-2y^2/x^2-2xy+y^2
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已知x^2-2xy-3y^2=0,求x^2+xy-2y^2/x^2-2xy+y^2
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已知x^2-2xy-3y^2=0,
即(x-3y)(x+y)=0所以x-3y=0或x+y=0
求x^2+xy-2y^2/x^2-2xy+y^2
=(x-y)(x+2y)/(x-y)(x-y)
=(x+2y)/(x-y)
当x-3y=0即x=3y时,原式=5y/2y=2.5
当x+y=0x=-y时,原式=y/(-2y)=-0.5
即(x-3y)(x+y)=0所以x-3y=0或x+y=0
求x^2+xy-2y^2/x^2-2xy+y^2
=(x-y)(x+2y)/(x-y)(x-y)
=(x+2y)/(x-y)
当x-3y=0即x=3y时,原式=5y/2y=2.5
当x+y=0x=-y时,原式=y/(-2y)=-0.5
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