(2x-3y)^2-(x-2y)(x-5y)-(2x+y)(2x-y)
=4x^2+9y^2-12xy-(x^2-2yx-5yx+10y^2)-(4x^2-y^2)
=4x^2+9y^2-12xy-x^2+2yx+5yx-10y^2-4x^2+y^2
=-5xy-x^2
当x=-2 y=-2/5时
原式=-4-4=-8
(2x-3y)^2-(x-2y)(x-5y)-(2x+y)(2x-y)
=4x^2+9y^2-12xy-(x^2-2yx-5yx+10y^2)-(4x^2-y^2)
=4x^2+9y^2-12xy-x^2+2yx+5yx-10y^2-4x^2+y^2
=-5xy-x^2
当x=-2 y=-2/5时
原式=-4-4=-8