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2x 3y 2 28x 2y 4xy

-2x³y²+28x²y-4xy =-2xy(x²y-14x+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

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&...

因为|x-a|和(y+4)方都是大于等于0的。要想|x-a|+(y+4)方=0成立只有|x-a|=0和(y+4)方=0,所以可以知道x=a,y=-4; A-2B=6x+3=3a;结合x=a可以求得x的值为-1 然后A的值就可以求出来了..

(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.

x2+4xy+4y2x?3y÷x2?4y23x?6y+x3y?x=(x+2y)2x?3y?3(x?2y)(x+2y)(x?2y)-xx?3y=3(x+2y)x?3y-xx?3y=2x+6yx?3y,∵x:y=3:5且x≠0.∴设x=3k,y=5k,原式=6k+30k3k?15k=-3.

1、2x²(y+2)-3y²(x-3)-12xy =2x²y+4x²-3xy²+9y²-12xy = 2、x²-4xy+4y²-6x+12y+8 =(x-2y)²-6(x-2y)+8 =(x-2y-2)(x-2y-4) 3、x²-(2a+1)x-3a(a-1) =(x-3a)(x+a-1)

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

A、xn(xn-x2+3)=x2n-xn+2+3xn,正确;B、应为(2x+3y)(-4xy)=-8x2y-12xy2,故本选项错误;C、应为(-2xy2-4x2y)(-3xyz)=6x2y3z+12x3y2z,故本选项错误;D、应为(xyz-7x2y+1)(-xz)=-x2yz2+7x3yz-xz,故本选项错误.故选A.

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