已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² 已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² + xY- 2Y² =求x² - 4x Y+ Y² =

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已知x²-XY=2,Y²-XY=5,求x²-4xY+Y²=2x²+xY-3Y²=x²已知x²-XY=2,Y²-

已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² 已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² + xY- 2Y² =求x² - 4x Y+ Y² =
已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x²
已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² + xY- 2Y² =
求x² - 4x Y+ Y² =

已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² 已知x² -XY = 2,Y² -XY= 5,求x² - 4x Y+ Y² = 2x² + xY -3Y² = x² + xY- 2Y² =求x² - 4x Y+ Y² =
2x^2+xy-3y^2
=2x^2-2xy+3xy-3y^2
=2(x^2-xy)-3(y^2-xy)
=2×2-3×5
=-11
x^2+xy-2y^2
=x^2-xy+2xy-2y^2
=(x^2-xy)-2(y^2-xy)
=2-2×5
=-8