作业帮5x=0.8y则x:y=
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令a=x+2yb=3x-ya/2+b/3=5(1)0.2a+0.8b=4(2)所以a=20-4b代入(1)10-2b+b/3=55b/3=5b=3a=20-4b=8所以x+2y=8(3)3x-y=3(
√X和√Y必须要有意义.所以X,Y≥0.所以只有X,Y=0,X+根号X+根号Y+Y才等于0,所以答案为0
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
已知3X=5Y,则X:Y=5:3再问：3X-5Y,��X:Y=
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=2,Y=3或X=3,Y=2
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
3x+4y=x+2y+62x-x+4y-2y=62x+2y=6x+y=6/2x+y=3
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
1.1/x+1/y=(x+y)/xy=-1/(x+y)去分母可得,（x+y)^2+xy=0即x^2+y^2=-3xy所以y/x+x/y=(x^2+y^2)/xy=-32.由1/x-1/y=5可得y-x
3x-5y=0,则x+y/x=（8/5）,x-y/y=（2/3）,2x-3y/2x+3y=(1/19)因为3x-5y=0所以3x=5y设x=5,y=3,可以解得3x-5y=0,则x+y/x=（8/5）
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^
用switch写：functiony=f(x)flag=(x>-5)*(x0)*(x-5)&&(x0)&&(x
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
x：y=7:5