x:y=7:3,x:y=5:3

|x|=3x=3或-3|y|=5y=5或-5|x-y|=|x|+|y||x|=3|y|=5|x|+|y|=8|x-y|=8x-y=8或-8由此可得y=5x=-3或y=-5x=3x+y=2或-2x-y=

x-y/7-x+y/10=1/2两边乘7010x-10y-7x-7y=353x-17y=35(1)2(x-y)+5(x+y)=32x-2y+5x+5y=37x+3y=3(2)(2)*3-(1)*79y

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

y-x=3(1)7x+5y=-9(2)(1)*7+(2)12y=12y=1x=-2

y=3x/5原式=x/(x+3x/5)+(3x/5)/[x-3x/5]-(9x^3/25)/(x^3-9x^3/25)=8/3-3/2-9/16=29/48

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+7y=y-3x∴x＝−32y∴x2−y2x2+y2=94x2− y294x2+y2=513故答案为513

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

x-y=1,x+y=-73（x+y)+20(x-y)-5=3×（-7）+20×1-5=-21+20-5=-6

(7y-3x)-(8y-5x)=7y-3x-8y+5x=2x-y

x=-2.5y=-3再问：过程再答：2x+y/3-2y=0①2(2x+y)-5=7y②展开②式，4x+2y-5=7y，移项整理的得4x-5y=5③将①整理得2x-5y/3=0④将④×2得4x-10y/

①x+y=5②3x-7y=11将①×7得：③7x+7y=35用②+③得：④3x-7y+7x+7y=11+35,即10x=46,即x=4.6代入①得：y=5-x=0.4

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

若(x-y)/(x+y)=3那么x-y=3(x+y)x-y=3x+3y故x=-2y所以(x+2y)/(6x-7y)=(-2y+2y)/(6*(-2y)-7y)=0如果不懂,请Hi我,祝学习愉快!

（5x+3y)(3y-5x)-(4x-y)(4y+x)=(3y)^2-(5x)^2-(4x^2+15xy-4y^2)=9y^2-25x^2-4x^2-15xy+4y^2=13y^2-15xy-29x^

7x-5y=33x+y=515x+5y=2522x=28x=14/11y=13/11

y=x+3代入7x+5y=9得7x+5x+15=9x=-0.5代入y=x+3得y=2.5∴﹛x=-0.5,y=2.5是原方程组的解再问：{3x+4y=16,5x-6y=33再答：{3x+4y=16（1

先将第一条式子移项得到7x-5x+x=3y/5+y/2-y/3（右边通分）得到x=23y/90(1)第二式子两边同乘以15得到15x=15y+8(2)把（1）代入（2）中得到的结果自己算啊!

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