3x+5y＝19 4x-3y＝6 解方程组

用换元法,设x+y=s,x-y=t,则原方程组为,s/2+t/3=6,①4s-5t=2,②将①×15+②,得,23s/2=92解得s=8,t=6即x+y=8,x-y=6两式加,得,x=7,y=1所以方

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

（x+y）/2+(x-y)/3=6①4(x+y)-5(x-y)=2②①*8得4(x+y)+8/3(x-y)=48③③-②得（8/3+5）(x-y)=46解得x-y=6④把x-y=6带入②解得x+y=8

2（x+2y）＝x²+y²+5整理得(x-1)^2+(y-2)^2=0x=1,y=2(x²+y²)/(3x-4y)=-1

3x^2(x-y)+6x(y-x)=3x^2(x-y)-6x(x-y)=(x-y)(3x^2-6x)=3x(x-y)(x-2)

可以得出x.x+y.y-6x-8y+25=x.x-6x+9+y.y-8y+16=(x-3).(x-3)+(y-4).(y-4)=0因为(x-3).(x-3)>=0,(y-4).(y-4)>=0所以x=

2(2x+3y)(3x+2y)-(6x-y)(2x-5y)=12x^2+26xy+12y^2-(12x^2-32xy+5y^2)=12x^2+26xy+12y^2-12x^2+32xy-5y^2=58

3*（4x+3y）=124*（3x+5y）=-24下式减去上式,得：11y=-36,则y可解,再带入原方程求出X

(y-x)(x-y)^3(y-x)^5=(y-x)[-(y-x)^3](y-x)^5=-(y-x)^(1+3+5)=-(y-x)^9=(x-y)^9

(x+y)-(2x+y/2)-(3x+y/6)-(4x+y/12)-(5x+y/20)-……-(10x+y/90)=x-2x-3x-4x-..-10x+y*(1-1/2-1/6-1/12-..1/90

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

(x-y)^8

(x-y)^5*(y-x)^3*(x-y)^2=-(x-y)^5*(x-y)^3*(x-y)^2=-（x-y）^(5+3+2)=-(x-y)^10

绝对值加平方=0因为两者均大于等于0所以都是0|x+y+2|=0(2x+3y+5)²=0x+y=-22x+3y=-5x=-1y=-1有什么不明白可以继续问,随时在线等.

=exp1,exp2------r=exp2逗号表达式从左往右执行,但返回的最后1个式子的值所以：y=（（x＝3*y,x＋6）,x－1）；-->y=(x=x+6,x-1)-->y=(x=20,13)-

x-5y＝13(1)3x+y＝20(2)(1)+(2)*5x-5y+15x+5y=13+10016x=113x=113/16y=20-3x=-19/16

(3x-4y)(5x-4y)-(7x-8y)(6y-5x)=15x²-12xy-20xy+16y²-（42xy-35x²-48y²+40xy）=15x²

①×2-②得，-7y=5，解得y=-57，代入①得，x-3×（-57）=5，解得x=207．故原方程组的解为x＝207y＝−57．再问：非常感谢

(2X-3y)-(5x-y)=2x-3y-5x+y=2x-5x-3y+y=(2x-5x)+(-3y+y)=-3x-2y这样写总是全过程了吧

x＋3y＋|3x－y|＝192x＋y＝6可知y=6-2x：代入上式可得x+3(6-2x)+|3x－(6-2x)|=19化简计算后可知：|5x-6|=1+5x可知5x-6=1+5x或5x-6=-(1+5