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2x 3y 2 28x 2y 4xy

4x^2+y^2+4xy+6x+3y-28 =(2x+y)^2+3(2x+y)-28 =(2x+y+7)(2x+y-4) (x+y)^2-4(x^2-y^2)-21(x-y)^2 =(x+y)^2-4(x+y)(x-y)-21(x-y)^2 =[(x+y)-7(x-y)][(x+y)+3(x-y)] =(x+y-7x+7y)(x+y+3x-3y) =(-6x+8y)(4x-2y) =4(-3x+4y)(2x-y)

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

x^4-2*x^2*y^2-4*x*y^3+4*x^3*y+y^2*(4*x^2+(3/4)*y^2) =1/4*(2*x^2+4*x*y-3*y^2)*(2*x^2+4*x*y-y^2)

方程组化为:(x?3y)(x+y)=0(2x+y)2=4即x?3y=02x+y=2x?3y=02x+y=?2x+y=02x+y=2x+y=02x+y=?2解之得:x1=67y2=27x2=?67y2=?27x3=2y3=?2x4=?2y4=2.

设y'=p 则代入原方程得 p³-4xyp+8y²=0 ==>x=p²/4y+2y/p.(1) 令f(y,p)=p²/4y+2y/p ∵f'y=-p²/(4y²)+2/p f'p=p/(2y)-2y/p² ∴代入公式 (1-f'y*p)dy-f'p*pdp=0 得 [1+(p²/(4y²)-2/p)p]dy-[p/(2y)-2y/p&...

4x^2-4xy-3y^2-4x 10y-3 =(2x-3y)(2x y) (2x y)-6x 9y-3 =(2x y)(2x-3y 1)-3(2x-3y 1) =(2x-3y 1)(2x y-3) 用配

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

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