9 6y=6x,(3 16)y=16

(x+y)/6+(x-y)/10=3①(x+y)/6+(y-x)/10=-1②①可变为：(x+y)/6-（y-x)/10=3③②+③=(x+y)/3=2得x+y=6④②-③=（y-x）/5=-4得y-

看不懂.

解,由方程2可得：1/(x+y)=9/(x-y)-1---(1)所以4/(x+y)=36/(x-y)-4代入方程1,得42/(x-y)=7所以x-y=6代入(1)式得x+y=2联立可得x=4,y=-2

（用换元法）设A=x+y,B=x-y原方程组可化为2A-3B=1,6A+7B=51解得A=5,B=3即x+y=5,x-y=3解得x=4,y=1

x+y)(x-y)+(x-y)^2-(6x^2y-2xy^2)/2y=x^2-y^2+x^2-2xy+y^2-3x^2+xy=-x^2-xy=-(-2)^2-(-2)(1/3)=-4+2/3=-10/

原方程组变形得：①3﹙x＋y﹚－﹙x－y﹚=4②3﹙x＋y﹚＋﹙x－y﹚=6∴①＋②得：③x＋y=10／3②－①得：④x－y=1∴③＋④得：x=13／6③－④得：y=7／6∴x=13／6,y=7／6.

第一个两边乘128(x-y)-3(x+y)=-128x-8y-3x-3y=-125x-11y=-12(1)第二个6x+6y-8x+4y=16-2x+10y=16x-5y=-8(2)(1)-(2)×55

一式乘3减二式得x-y=-3带x-y入两式你应该会做了

①－②可得：x-y/10－y-x/10=4x-y／5＝4x-y＝20——③①＋②可得：x+y/3=2x+y=6——④由③④可得：x=13,y=－7

由(1)得xy+x-y-1=xy+x+y+1-2y=2∴y=-1把y=-1代入(2)得x(2-1)-6=-1(x-4)x-6=-x+4∴x=5∴方程组的解是x=5y=-1

2(x-y)/3-x+y/4=-1（1）6(x+y)-4(2x-y)=16（2）（1）方程两边同乘以12得8（x-y）-3(x+y)=-12合并同类项得5x-11y+12=0(3)(2)合并同类项得1

7y(x-3y)²-2(3y-x)³=7y(x-3y)²+2(x-3y)³=(x-3y)²[7y+2(x-3y)=(x-3y)²(7y+2X

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

因为2(x+y)-3(x-y)=1所以2x+2y-3x+3y=1-x+5y=1x=5y-1因为6(x+y)+7(x-y)=51所以6x+6y+7x-7y=5113x-y=51将x=5y-1代入13x-

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

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

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

(x+y^2+3)dy=(x-y+1)dx或：xdy+ydx+(y^2+3)dy-(x+1)dx=d(xy)+(y^2+3)dy-(x+1)dx=0通解为：xy+y^3/3+3y-x^2/2-x=C

很累-3x-2y