如果x y=4 3,求3x²-5xy 2y² 2x² 3xy-5y²的值

xy/x+y=3则xy=3(x+y)2x-5xy+2y/x-3xy+y=2(x+y)-5xy/(x+y)-3xy=2(x+y)-15(x+y)/(x+y)-9(x+y)=-13(x+y)/-8(x+y

x-y=2xy3x-5xy-3y/x+xy-y=[3(x-y)-5xy]/[(x-y)+xy]=(6xy-5xy)/(2xy+xy)=1/31/x+1/y=4y+x=4xyx-5xy+y/2x+xy+

(x^2+xy+2y^2)/(x^2-xy+y^2)=[(x/y)²+(x/y)+2]/[(x/y)²-(x/y)+1]分子分母同时除以y²=(4/9+2/3+2)/(4

xy/x+y=3xy=3(x+y)3x-5xy+3y/-x+3xy-y=(3x+3y)-5*3(x+y)/[-x-y+3*3(x+y)]=-12(x+y)/8(x+y)=-3/2望采纳,谢谢!

x^2+xy+y=14y^2+xy+x=28两式相加x^2+y^2+2xy+x+y=42(x+y)^2+(x+y)-42=0(x+y-6)(x+y+7)=0x+y=6或x+y=-7

上下都除以y^2

因为X+Y分之XY=2,所以XY=2(X+Y)代入后面的分子式得：13（X+Y)/5(X+Y)=13/5

X/Y=4/3设X=4k,Y=3k,k≠0则(3X^2-5XY+2Y^2)/(2X^2+3XY-5Y^2)=(3*(4k)^2-5*(4k)*(3k)+2*(3k)^2)/(2*(4k)^2+3*(4

(5x-xy+5y)/(3xy-x-y)=[5(x+y)-xy]/[3xy-(x+y)]=[5(x+y)-2(x+y)]/[6(x+y)-(x+y)]=1/2

如果x/y=3/4,求（3x的平方-5xy+2y的平方）/（2x;的平方+3xy-5y的平方因为x/y=3/4,设y=4t（t≠0）,则x=3t所以（3x²-5xy+2y²）/（2

1/x-1/y=2(y-x)/xy=2y-x=2xy(3x+5xy-3y)/(x-xy-y)=[5xy-3(y-x)]/[-xy-(y-x)]=(5xy-6xy)/(-xy-2xy)=-xy/-3xy

xy/x+y=3xy=3（x+y）3x-5xy+3y/-x+3xy-y=3x-15（x+y）+3y/-x+9（x+y）-y=-12(x+y)/8（x+y）=-3/2

xy/(x+y)=2,1/x+1/y=2(3x-5xy+3y)/(-x+3xy-y)=(3/y+3/x-5)/(-1/y-1/x+3)=(6-5)/(-2+3)=1题目错了,应该是-5xy,不是-5y

x：y=2:3设x=2k,则y=3k∴x²+xy+2y²/x²-xy+y²=(4k²+6k²+9k²)/(4k²-6k&

已知xy+x+y=6则xy+x+y+1=（x+1）（y+1）=7=7×1因为x,y都是自然数（非负整数）所以x+1,y+1≥1所以只能x+1=7y+1=1即x=6,y=0或x+1=1,y+1=7即x=

3(x^2-xy)-xy+y^2=3(x^2-xy)-(xy-y^2)=3*5-(-3)=15+3=18

xy/(x+y)=2xy=2(x+y)(3x-5xy+3y)/(-x+2xy-y)=[3(x+y)-5xy]/[2xy-(x+y)]=[3(x+y)-10(x+y)]/[4(x+y)-(x+y)]=-

XY/X+Y=2∴xy=2(x+y)3X-5xY+3Y/-X+3XY-Y=[3(x+y)-5xy]/[-(x+y)+3xy]=[3(x+y)-10(x+y)]/[-(x+y)+6(x+y)]=-7/5

x+y=5xy（2x-3xy+2y)/(x+2xy+y）=[2（x+y）-3xy]/[(x+y)+2xy]=(2×5xy-3xy)/(5xy+2xy)=7xy/7xy=1再问：若x＋1/x＝3,求(x