A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x

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A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当xA=x^2+3xy-y^2,B=-2x^2+xy-y^2.当xA=x^2+3xy-y^2,B=-2x^2+xy-y^2.当xA-B=(x^

A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x
A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x

A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x
A-B=(x^2+3xy-y^2)-(-2x^2+xy-y^2)
=x²+3xy-y²+2x²-xy+y²
=3x²+2xy
∵x0
即A-B>0
∴A>B

A-B=3x^2+2xy
因为x0,所以 A-B=3x^2+2xy>0,即 A>B