(5xy-3x^2+3)+2(y^2-xy+x^2)-(3xy+2y-x^2+3)
=5xy-3x^2+3+2y^2-2xy+2x^2-3xy-2y+x^2-3
=(5xy-2xy-3xy)+(2x^2-3x^2+x^2)+2y^2-2y+3-3
=0+0+2y^2-2y+0
=2y^2-2y
没有x
所以值与X无关