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先化简再求值2x^2y%4xy^2%2分之1xy^2 x^2y其中x=负...

1、反推回去题目应该这样吧求3x^2y-{6xy-2(4xy-2)-x^2y}+1的值,其中x=-1/2,y=1 原式=3x^2y-(6xy-8xy+4-x^2y)+1 =3x^2y-(-2xy+4-x^2y)+1 =3x^2y+2xy-4+x^2y+1 =4x^2y+2xy-3 =4*1/4*1+2*(-1/2)*1-3 =1-1-3 =-3 2、x=0时,该代数式的值为—1 ax的...

=4xy-[x²+5xy-y²-x²-3xy+2y²] =4xy-2xy-y² =2xy-y² =2*(-1/4)*(-1/2)-(-1/2)² =0

原式=(x-2y)^2/(x-2y)-(2x-3y)(2x+3y)/(2x-3y) 分式上下约分=x-2y-(2x+3y) =-x-5y 代入数值=-5

原式=4x2y-[6xy-(8xy-4)-x2y]+1,=4x2y-(6xy-8xy+4-x2y)+1,=4x2y-6xy+8xy-4+x2y+1,=5x2y+2xy-3,把x=12,y=2代入上式得:原式=5x2y+2xy?3=?52.

该题一看题目,肯定是利用完全平方来解决,根据问题最大,就按那个方向凑一个完全平方,然后解下去 x²-4xy+4y²+4x²y²=4 (x²+4xy+4y²)+(-8xy+4x²y²+4)=8 (x+2y)²+4(xy-1)²=8 从上面可以...

如图所示:

由已知得x²+y²-2xy+﹙xy﹚²-2xy+1=0 ∴﹙x-y﹚²+﹙xy-1﹚²=0 ∴x-y=0且xy=1 ∴x=y=±1

(1)12xy/5a÷8x^2y =3/10ax (2)1- [x-y]/x+2y÷x^2-y^2/x^2+4xy+4y^2 =1-(x-y)/x+2y*(x+2y)^2/(x+y)(x-y) =1-[x+2y/x+y] (3)(-ax^4y^3)÷(5/6ax^2y^2) =-6/5ax^4y^3/ax^2y^2 =-6/5x^2y (4)(-2a^3b^2)^3÷(-3ab^3)^2= =-8a^9b^6/6a^2b^6 =-4/3a^7 (5)...

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