A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x
问题描述：
A=x^2+3xy-y^2,B=-2x^2+xy-y^2.当x
答
A-B=3x^2+2xy
因为x
答
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