2x²+(-x²-2xy+2y²)-3(x²-xy+2y²),其中x=2,y=-1/2

2x²+(-x²-2xy+2y²)-3(x²-xy+2y²),其中x=2,y=-1/2
2x²+(-x²-2xy+2y²)-3(x²-xy+2y²),其中x=2,y=-1/2

2x²+(-x²-2xy+2y²)-3(x²-xy+2y²),其中x=2,y=-1/2
2x²+(-x²-2xy+2y²)-3(x²-xy+2y²),
=2x²-x²-2xy+2y²-3x²+3xy-6y²
=-2x²+xy-4y²
当x=2,y=-1/2时
原式=-8-1-1
=-10

原式=2x²-x²-2xy+2y²-3x²+3xy-6y²
=-2x²+xy-4y²
当x=2,y=-1/2时
原式=-2*2²+2*(-1/2)-4*(-1/2)
=-8-1+2
=-7