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xy y 2xy 3x y y 2y 1

(1)x2+4x-3x2-5x+6x2-1=x2-3x2+6x2-5x+4x-1=4x2-x-1,当x=-1时,原式=4×(-1)2-(-1)-1=4;(2))(3x2y-2xy)2-(xy2-2x2y)=9x4y2-12x3y2+4x2y2-xy2+2x2y,当x=-1,y=2时,原式=9×(-1)4×22-12×(-1)2×22+4×(-1)2×22-(-1)×22+2×(-...

(x+1)/x-(y+1)/y=3 1+1/x-1-1/y=3 1/x-1/y=3 (x-y)/xy=-3 x-y=-3xy 原式=(3x-2xy-3y)/(2x+3xy-2y) =(-9xy-2xy)/(-6xy+3xy) =11/3

后面那个是。前面的式子x-y+xy=1中的xy是二次的,所以是二元二次方程。

(3x²y-xy²+1/2xy)÷(-1/2xy) =xy(3x-y+1/2)÷(-1/2xy) =-2(3x-y+1/2) =-6x+2y-1

[5xy^2(x^2-3xy)-(-3x^2y^3)^3]除(1/2xy)^2 =[5x²y²(x-3y)+27x^6y^9]÷(1/4*x²y²) =[5x²y²(x-3y)+x²y²(27x^4y^7)]÷(1/4*x²y²) =4[5(x-3y)+27x^4y^7] =20x-60y+98x^4y^7 ∵x+y=4,x^2+y^2=14, ∴2...

(1)原式=-2x3+4x-x2-x-3x2+2x3=-4x2+3x,当x=-3时,原式=-4×(-3)2+3×(-3)=-36-9=-45;(2)原式=2x2-x2-2xy+2y2-2x2+2xy-4y2=-x2-2y2,∵(x-3)2+|y+2|=0,∴x=3,y=-2,当x=3,y=-2时,原式=-32-2×(-2)2=-17;(3)原式=x+3y-3xy-2xy+4x...

解: 若y=0,则等式3xy+z²+1=0变为z²+1=0 z²=-1,平方项恒非负,z无解,因此y≠0 y-3x=2,等式两边同乘以y,得:y²-3xy=2y y²-3xy+3xy+z²+1=2y (y²-2y+1)+z²=0 (y-1)²+z²=0 平方项恒非负,因...

1, (x^2-3xy+2y^2) / (2x^2-3xy+7y^2) =(x-2y)(x-y)/[(2x-y)(x-y)+6y^2], 由x/y=2/7,得: 7x=2y, 所以x-y=-5y/7, x-2y=-12y/7, 2x-y=-3y/7, 所以原式=[(-12y/7)(-5y/7)]/[(-3y/7)(-5y/7)+6y^2] =(60/49)/[(15/49)+6] =60/309=20/103。 或...

x,y满足等式2(x-1/2)2+∣y-1∣=0 x-1/2=0 y-1=0 x=1/2 y=1 A=3x2-xy+y2,B=2x2-3xy+2y2, 3B-2A =3(2x^2-3xy+2y^2)-2(3x^2-xy+y^2) =6x^2-9xy+6y^2-6x^2+2xy-2y^2 =-7xy+4y^2 =-7*(1/2)*1+4*1^2 =-7/2+4 =1/2

(1)1/2x^2y+1/2xy^2=(X+Y)/(X^2Y^2)=6/(10*10)=3/50(2)3x+5y=-2 5y= -3x-2 y= -3x/5-2/5

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