解5x-2y=20,2x-5y=40

设（x+y）为t,(x-y)为p,所求的解为c所以t/2+p/2=64t-5p=c整理得：5t+5p=604t-5p=c两式相加得9t=60+cc=9t-60所以4(x+y)-5(x-y)=9(x+y

设x-y=mx+y=n则6m-2n=143m+n=5解得m=2n=-1即x-y=2x+y=-1解得x=1/2y=-3/2

5x+y=369y-x=2即45y-10+y=36y=1x=7

化简得：-x+7y=11①7x+3y=27②①式×7得：-7x+49y=77③②+③得：52y=104∴y=2代入①得：x=3∴x=3,y=2再问：亲，是代入法哦！再答：代入法①式得3x+3y-4x+

x-y/5y=(x-y)(x-y)/(5y(x-y))=(y-x)^2/(5y(x-y))

因为(x-y)/(x+y)=3,则(x＋y)/(x－y)＝1/3则5(x-y)(x+y)-(x+y)/2(x-y)＝5*3-1/(3*2)=15-1/6=89/6

｛5（x＋y）＋3（x－y）＝2｛7（x＋y）－3（x－y）＝－6原方程组化简得﹛4x+y=1(1)2x+5y=-3(2)(1)×5得20x+5y=5(3)(3)-(2)得18x=8x=4/9代入（1

化简x+y=105x+7y=625x+5y+2y=622y=62-50y=6x=4

2/(x+y)+5/(x-y)=189/(x+y)-10/(y-x)=66设x+y=a,x-y=b,原方程化为2/a+5/b=18-----1(1)9/a+10/b=66-------(2)(2)-(

X^2表示平方X^2+4X+4+Y^2-2Y+1=0(X+2)^2+(Y-1)^2=0因为平方大于=0所以X+2=0Y-1=0X=-2Y=1X^2+Y^2=5

另a=1/（x+y）,b=1/(x-y);则2a+5b=18；9a+10b=66；解得a=6,b=6/5；即       &nbs

(x+y)/2+(x-y)/3=6①5(x+y)-2(x-y)=4②由①得3x+3y+2x-2y=365x+y=36y=36-5x③由②得5x+5y-2x+2y=43x+7y=4④③代入④得3x+25

设a=x+y,b=x-y原方程组为：a/2+b/3=6,即3a+2b=36,即：12a+8b=1444a-5b=12,即：12a-15b=36相减得：23b=108,得：b=108/23,再得：a=1

方程化为－x+7y=1117x+3y=272将1式化为x=7y-113则将3式代入2式可得7（7y-11）+3y=2752y=104y=2x=7×2-11x=3所以解得x＝3y＝2

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

{(x-2)(y+3)=(x+1)(y-1){(x+1)(y+1)=(x-1)(y+5){xy+3x-2y-6=xy-x+y-1{xy+x+y+1=xy+5x-y-5{4x-3y=5(1){4x-2y

先将第一个等式整理得12X+Y=36,第二个等式整理得-X+9Y=2,由第一个等式得Y=36-12X,通过换元法得-X+9(36-12X)=2,解出X=322/109,再把X=322/109代入-X+

化简得：-x+7y=11①7x+3y=27②①式×7得：-7x+49y=77③②+③得：52y=104∴y=2代入①得：x=3∴x=3,y=2

2x+y=2(1)-x+y=5(2)3x=-3x=-1y=4

展开x^2-2y^2-xy=-5x^2-2y^2+xy=7所以x^2-2y^2=1xy=6上式除以下式,解分式方程x/y=3/2或-4/3(舍去)所以x^2=9y^2=4x=3y=2或x=-3y=-2