3y-xy x平方-3x,其中x=负1,y=2

原式=2x²y+2xy-3x²y+3xy+4x²y=3x²y+5xy=3×1²×(-1)+5×1×(-1)=-3-5=-8

(x-y)分之(x²+y²)+(y-x)分之(2x-y),其中x=3+√2,y=3-√2=(x²+y²)/(x-y)-(2x-y)/(x-y)=(x²

（3x-y)的平方-（2x+y)的平方-5x(x-y)=(3x-y+2x+y)(3x-y-2x-y)-5x(x-y)=5x(x-2y)-5x(x-y)=5x(x-2y-x+y)=5x*(-y)=-5x

[(X+2Y)平方-(X+Y)(3X-Y)-5Y平方]除以（2X）=(x²+4y²+4xy-3x²+xy-3xy+y²-5y²)/(2x)=(-2x&

[(x+2y)^2-(x+y)(3x-y)-5y^2]/2x=(x^2+4xy+4y^2-3x^2-3xy+xy+y^2-5y^2)/2x=(-2x^2+2xy)/2x=-x+y=2+1/2=二分之五

【1-2x/(x+y)】÷(x^2-2xy+y^2)/(3x+3y)+(x^2+xy)/(x^2-y^2)=(x+y-2x)/(x+y)÷(x-y)^2/3(x+y)+x(x+y)/(x+y)(x-y

y是多少原式=(x+y)(x-y)/(x-y)²+x(y+3)/x(y+3)=(x+y)/(x-y)+1=(x+y+x-y)/(x-y)=2x/(x-y)=1/(1/2-y)再问：y=3

原式=5x²-3y²-(5x²-3xy-y²-x²+3xy-3y²)=5x²-3y²-(4x²-4y²

原式=(3x²-2x²-2xy+2xy-y²)÷(x+y)=(x²-y²)÷(x+y)=(x+y)(x-y)÷(x+y)=x-y=1/2-1/3=1/

=3x平方y-2x平方y+6xy-3x平方y+xy=-2x平方y+7xy=-2*1*(-2)+7*(-1)*(-2)=4+14=18

∵xyx+y=-2，yzy+z=43，zxz+x=-43，∴1x+1y=-12，1y+1z=34，1z+1x=-34，∴2（1x+1y+1z）=-12，即1x+1y+1z=-14，则xyzxy+yz+

(2x-3y)的平方-(2x+3y)的平方=[(2x-3y)+(2x+3y)][(2x-3y)-(2x+3y)]=4x*(-6y)=-24xy∵x=1/6,y=1/8∴原式=-24*1/48=-1/2

5xy平方-2x平方y+[3xy平方-(4xy-2x平方y-2x平方y)]＝5xy平方-2x平方y+[3xy平方-4xy＋2x平方y＋2x平方y)]＝5xy平方-2x平方y+3xy平方-4xy＋2x平

2（x²y+xy）-3（x²y+xy）-4x²y=-（x²y+xy）-4x²y=-5x²y-xy=-xy（5x+1）=1×2（-5+1）=-

/>原式=[y/(x-y)]+[y³/(x³-2x²y+xy²)]÷[(xy+y²)/(y²-x²)]=[y/(x-y)]+{y&

x的平方-(2x的平方-xy+y的平方)+(-x的平方+3xy+2y的平方)=x²-2x²+xy-y²-x²+3xy+2y²=-2x²+4x

解(x-y)(x+y)-(x-2y)²+x(3x-5y)-(x-y)(x-2y)=(x²-y²)-(x²-4xy+4y²)+(3x²-5xy

x=±1,y=±3,z=±2xyzz>y则0>x>z>yx=-1,y=-3,z=-2,x2y-[4x2y-(xyz-x2z)-3x2z]-2xyx=x2y-4x2y+xyz-x2z+3x2z-2xyx

3y平方-x平方+(2x-y)-(x平方+3y平方)=3y²-x²+2x-y-x²-3y²=-2x（x-1）-y当x=1,y=－2时原式=-2×1×（1-1）-

2xy/(x^2-y^2)-x/(x+y)+y/(y-x)=2xy/(x^2-y^2)-x/(x+y)-y/(x-y)=2xy/[(x-y)(x+y)]-x(x-y)/[(x-y)(x+y)]-y(x