4xy-{(x^2+5xy-y^2)-(x^2+3xy-2y^2)}其中x=-1/4y=-1/2

4xy-{(x^2+5xy-y^2)-(x^2+3xy-2y^2)}其中x=-1/4y=-1/2
4xy-{(x^2+5xy-y^2)-(x^2+3xy-2y^2)}其中x=-1/4y=-1/2

4xy-{(x^2+5xy-y^2)-(x^2+3xy-2y^2)}其中x=-1/4y=-1/2
因为x=-1/4,y=-1/2,所以：
4xy-{(x²+5xy-y²)-(x²+3xy-2y²)}
=4xy-(x²+5xy-y²-x²-3xy+2y²)
=4xy-(2xy+y²)
=2xy-y²
=y(2x-y)
=(-1/2)*[2*(-1/4)-(-1/2)]
=(-1/2)*0
=0