已知x分之y=5 求x平方-3xy-y平方分之3x平方 5xy-3y平方

（1）x^2+3xy-4y^2=0十字相乘：(x+4y)(x-y)=0则：x=-4y,或x=y；当x=-4y时,(x-2y)/(x+2y)=-6y/(-2y)=3；当x=y时,(x-2y)/(x+2y

原式＝(x^2-2x+1)+(y^2-4y+4)=(x-1)^2+(y-2)^2=0,所以x=1,y=2,代入问题得结果为3/2

x-3y=0x=3y(2x+y)/(x^2-2xy+y^2)÷1/(x-y)=(2x+y)/(x-y)^2÷1/(x-y)=(2x+y)/(x-y)^2*(x-y)=(2x+y)/(x-y)=(2*3

3x^2+xy-2y^2=(3x-2y)(x+y)=0x=-2y/3,或x=-y但由于你要求的式子中分母里有X平方-Y平方x=-y舍去其他就代入吧

x/y=2平方x²/y²=4原式分子分母同除以y²所以原式=(x²/y²-x/y+3)/(x²/y²+x/y+6)=(4-2+3)

令x=y+3变成x-y=3把x-y=3带到x-y里4分之一(x-y)的平方-0.3(x-y)+0.75(x-y)的平方+10分之3(x-y=2.25-0.9+6.75+0.9=9

x=y+3∴x-y=34分之一(x-y)的平方-0.3(x-y)+0.75(x-y)的平方+10分之3(x-y）-2（x-y）+7=(0.25+0.75)(x-y)²+(-0.3+0.3-2

(x-y)/(x+y)=(x-y)(x+y)/[(x+y)^2]=(x^2-y^2)/[x^2+y^2+2xy]=2xy/[x^2+y^2+x^2-y^2]=2xy/(2x^2)=y/xx^2-y^2

2x-y+1的绝对值+（3x+2分之3y）平方=0则2x-y+1=03x+3y/2=0,则2x-y=-1①2x+y=0②①+②,得4x=-1,则x=-1/4①-②,得-2y=-1,则y=-1/2x+y

x/y=7/2(x²-3xy+2y²)/(x²+2xy+y²)=[(x/y)²-3(x/y)+2]/[(x/y)²+2(x/y)+1]=[(

已知5x-4y=0,切xy≠0,x/y=4/5;求(x平方-y平方)分之(x平方+y平方)-(x-y)分之(x+y)的值=(x²+y²)/(x²-y²)-(x+

y=2x/3则xy=2x2/3y2=4x2/9所以原式=(2x2/3)/(x2+4x2/9)-(4x2/9)/(x2-4x2/9)=(2/3)/(1+4/9)-(4/9)/(1-4/9)=6/13+4

因为x²+y²-4x+2y+5=0所以(x²-4x+4)+(y²+2y+1)=0所以(x-2)²+(y+1)²=o所以x=2y=-1所以下面

x的平方+y的平方=2xyx的平方+y的平方-2xy=0(x-y)^2=0x=y3x+y分之15x-y=14x/4x=7/2

x=5y所以原式=(25y²-10y²+3y²)/(100y²+25y²-6y²)=18y²/119y²=18/119

把4拆成3+1(x²-2√3x+3)+(y²+2y+1)=0(x-√3)²+(y+1)²=0平方大于等于0相加等于0,若有一个大于0,则另一个小于0,不成立.所

若x且y不等于0,则2*x^2-5x*y+3y^2=0等式两边同除以x*y,得2x/y-5+3y/x=0,设x/y=a,则2a-5a+3/a=0,化为二次函数的一般形式：2a^2-5a+3=0,因式分

2x²-xy-3y²=0(x+y)(2x-3y)=0x=-y(舍去)或x=3y/2x/y=3/2x/y-x²/(x-y)=x/y-x²/(x²-2xy

x²+y²=-2xyx²+2xy+y²=0(x+y)²=0x+y=0所以x=-y所以(x-3y)/(x+3y)=(-y-3y)/(-y+3y)=-4y

1.整理得到算式[2x-x+y]/[x^2-y^2]=[x+y]/[x+y][x-y]=1/[x-y]代入得到1/72.整理得到[1-3/(a+2)]/[(a^2-2a+1)/(a^2-4)]=[(a