3x-y=8 2x y=7

已知x/y=7/2,(2x²+3xy+2y²)/(x²+2xy+y²)=(2x/y+3+2y/x)/(x/y+2+y/x)=(2×7/2+3+2×2/7）/（7

(x^2-3XY+2Y^2)/(X^2-2XY+Y^2)=(x-2y)(x-y)/(x-y)^2=(x-2y)/(x-y)=(x-y-y)/(x-y)=1-y/(x-y)=1-1/(x/y-1)=1-

xy^2=-6(xy^2)^2=(-6)^2即x^2y^4=36(xy^2)^3=(-6)^3即x^3y^6=-216-xy(x^3y^7-3x^2y^5-y)=-xy[(x^3y^6)*y-3(x^

楼主算得对,第一个回答在第二步的地方把三次方的系数3弄丢掉了,所以正确的还是-165

x-3xy-Y分之3x+5xy-3y==(3x+5xy-3y)/(x-3xy-Y)=(5+3*(1/y-1/x))/(-3+(1/y-1/x)).分子分母同时除以xy=(5-21)/(-3-7).将x

(-3x^y+2xy)-(4x^+xy)=-3x^y+2xy-4x^-xy=-3x^y+xy-4x^所以填上-3x^y+xy-4x^

原式=6x+4xy+2xy+3x+2y-4xy+7y=9x+9y+2xy=9(x+y)+2xy=9×4+2×2=36+4=40

5xy+4x+7y+6x-3xy-4xy+3y=5xy-3xy-4xy+4x+6x+7y+3y=（5-3-4）xy+（4+6）x+（7+3）y=-2xy+10x+10y=-2xy+10（x+y）因为x

（4xy+12y)+[7x-(3xy+4y-x)]=4xy+12y+7x-3xy-4y+x=xy+8x+8y=xy+8(x+y)=(-2)+8*3=-2+24=22

先把代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)化简（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)=5XY+4X+7Y+6X-3XY-4XY+3Y=-2XY+10X+1

最简单的方法就是用特殊值,令x=-2,y=1然后代入所求表达式,求出其值.为-8；另外此内题的另一个解法是变化所求表达式,使它变成关于xy^2的表达式.

（7xy+4x-7y）+(6x-3xy)-(3y+4xy)=7xy+4x-7y+6x-3xy-3y-4xy=10x-10y=10（x-y）=10*3=30

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

设X=kY.kY^2/(3k+2)Y=1/8kY^2/((2k+3)Y=1/7由上式得：3k+2=8kY,2k+3=7kY所以2/（8Y-3）=3/（7Y-2）所以Y=1/2,X=1

∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．

(5xy+4x+7y)+(6x-3xy)-(4xy-3y)=5xy+4x+7y+6x-3xy-4xy+3y=(5xy-3xy-4xy)+(4x+6x)+(7y+3y)=-2xy+10x+10y=-2x

因为x-y=-2xy所以将x-y都换成-2xy了

X+y=3xy=-5X-y=?(x-y)^2=(X+y)^2-4xy=9+20=29则x-y=±根号29

因为,x-y=3xy所以：-3x+6xy+3y/[(7x-5y)-9xy-(3x-y)]=[-3(x-y)+6xy]/[(7x-5y)-9xy-(3x-y)]=[-3*3xy+6xy]/[7x-5y-

[(x-y)^2+2xy-y^2]/[x^2+7xy+y^2]=[x²-2xy+y²+2xy-y²]/[x^2+7xy+y^2]=x²/[x^2+7xy+y^2