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2x 3y 2 28x 2y 4xy

原式==x^4+2x^2y+x^2y^2-4x^2y^2-4xy^3-y^4 =(x^2+xy)^2-(2xy+y^2)^2 =(x^2+xy+2xy+y^2)(x^2+xy-2xy-y^2) =(x^2+3xy+y^2)(x^2-xy-y^2)

解: (2x+y)²-(2x+3y)(2x-3y)-2(x-2y)² =(4x²+4xy+y²)-(4x²-9y²)-2(x²-4xy+4y²) =4x²+4xy+y²-4x²+9y²-2x²+8xy-8y² =-2x²+12xy+2y²

1/x - 1/y = 2 x-y = -2xy 2x-2y - 5xy = -9xy 3x-3y+4xy = -2xy 值=2/9

(1)[(3x+2y)2-(3x-2y)2+4xy]÷(-2x),=[6x?4y+4xy]÷(-2x),=-14y;(2)3y(4x-3y)(3y+4x)-(2x-3y)(4x2+6xy+9y2),=3y(16x2-9y2)-(8x3-27y3),=48x2y-27y3-8x3+27y3,=48x2y-8x3.

(1)原式=-2x-4x+2y+3x-2y+1=-3x+1,当x=-3时,原式=10;(2)原式=xy-2y2-8xy+6y2-2x2y+30y2-4x2y=-7xy+34y2-6x2y,当x=1,y=-2时,原式=162.

2x^2+4xy-3y^2=2(x^2-xy)+3(2xy-y^2)=2×(-3)+3×(-8)=-6-24=-30

2x^2-xy-3y^2=0 (2x-3y)(x+y)=0 x=3y/2 x=-y x^2-4xy+4y^2=1 (x-2y)^2=1 当x=3y/2 y=±2,x=±3 当x=-y y=±1/3 x=±1/3

x3y-4x2y2+4xy3=xy(x2-4xy+4y2)=xy(x-2y)2∵x=2y+1,∴x-2y=1,∴原式=2×12=2.

原式=3x2y-6y3+12xy2+6y3-12xy2-2x2y=x2y,当x=?12,y=4时,原式=(?12)2×4=14×4=1.

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