9y=3x-(x-1)

原式=x(1+2+3+……+9)+y(1+1/2+1/6+……+1/72)=45x+y(2-1/2+1/2-1/3+……+1/8-1/9)=45x+y(2-1/9),x=1,y=-9时原式=45-9（

（1+2+3+...+9）x+(1+(1-1/2)+(1/2-1/3)+...+(1/7-1/8)+(1/8-1/9))y=50x+(1+1-1/9)y=100+270=370

3(x+y)+3(y-x)=1(1)3(x+y)+4(y-x)=-1(2)(2)-(1)得y-x=-2(3)代入（1）3（x+y)-6=1x+y=7/3=>x=7/3－y又由（3）得x=y+2y+2=

设a=(x-1)(x-2)(x-3)(x-4)(x-5)(x-6)(x-7)(x-8)(x-9)那么y=a*(x-10);那么y^=a^*(x-10)+a*(x-10)^=a^*(x-10)+a那么y

[(2/3)x√(9x)+6x√(y/x)]+[y√(x/y)-x²√(1/x)]化简：原式=[(2/3)*3*x√x+6√(xy)]+[√(xy)-x√x]=2x√x+6√(xy)+√(x

1/9x^2-10/9xy+y^2-(1/9x^2-y^2)=-10/9xy+2y^2=2y(y-5/9x)

y=3/(x+1/x+1)x+1/x≤-2,所以x+1/x+1≤-1令t=x+1/x+1,则t≤-1,y=3/t值域为[-3,0)再问：你写的我看不大懂再问：一步步写再答：

3x+2y=13①3x-2y=5②由①+②,得6x=18,x=3x=3代入②,得y=2该方程组的解集为x=3,y=2x-y/3=x+y/2+1①2x-5y=9②由①,得-y/3=y/2+1,y=-6/

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

3(x+y)-4(x-y)=4(x+y)/2+(x-y)/6=1令a=x+y,b=x-y3a-4b=4(1)a/2+b/6=1则3a+b=6(2)(2)-(1)5b=2b=2/5a=(6-b)/3=2

4x=9yx=9/4*y(1)(x+y)/y=[(9/4)y+y]/y=(9/4+1)y/y=9/4+1=13/4(2)(y-x)/2x=[y-(9/4)y]/[2*(9/4)y]=(1-9/4)y/

令a=1/(x+y),b=1/(x-y)4a+6b=3(1)9b-a=1(2)(1)+(2)×46b+36b=3+442b=7b=1/6a=9b-1=1/2所以x+y=1/a=2x-y=1/b=6相加

{4/x+y+6/x-y=3{9/x-y-1/x+y=1令1/(x+y)=a,1/(x-y)=b则原方程组为{4a+6b=3{-a+9b=1解得{a=1/2{:b=1/6所以{x+y=2{x-y=6解

原式可以化为：y*x^2+(y-3)*x+1=0Δ=(y-3)^2-4y≥0解得y≥9或y≤1由于x

解9y=3x-(x-1)2x-9y+1=0①4(x+y)-(2x+4)=8y2x-4y-4=0②②-①得：5y-5=0∴y=1将y=1代入①得：2x-9+1=0∴x=4∴方程的解为：x=4,y=1

完整设1/(x+y)=a,1/(x-y)=b原方程组可变为4a+6b=39b-a=1a=9b-136b-4+6b=3b=1/6,a=1/2x+y=2x-y=6所以原方程组的解为：x=4,y=-2

把x=9y带入到3x=2y+1中得到3*(9y)=2y+127y=2y+125y=1y=1/25x=9y=9/25所以x=9/25,y=1/25

x+y=3则y=3-x带入x+2y=9解得x=-3,y=6剩下的都这样解

再答：