x y=3则4-2x-2y=多少-搜答案-搜狗做题网

你这道题是不是写错了?3y^3应该是3y^2?如果是的话,按照下面的去做2x^2-xy-3y^2=2(x^2+xy)-2xy-xy-3y^2=-2(x^2+xy)-3(y^2+xy)=2*3-3*(-

因为x-y=4xy所以x-2xy-y=2xy2x+3xy-2y=11xyx-2xy-y分之2x+3xy-2y=5.5

(-3x^y+2xy)-(4x^+xy)=-3x^y+2xy-4x^-xy=-3x^y+xy-4x^所以填上-3x^y+xy-4x^

y-x=3xyx-y=-3xy(x-2xy-y)/(2x-14xy-2y)=(-3xy-2xy)/(-3xy*2-14xy)=-5xy/(-20xy)=1/4

-5x+2-3xy-5y因为xy=1所以原式=-5x-5y-1-5（x+y)-1因为x+y=3所以-15-1=-16

（x平方+2xy-3y平方）除以（x-y)=(x-y)(x+3y)/(x-y)=x+3y=12

x²y-xy²=xy(x-y)=3×2=6再问：怎样变为xy(x-y)再答：提取公因式x²y＝(xy)×(x)xy²＝(xy)×(y)都有因式xy，可以提取出来

x²+xy=3两边同时乘以2得：2x²+2xy=6①xy+y²=-2两边同时乘以3得：3xy+3y²=-6②①-②得：2x²-xy-3y²=

（4xy+12y)+[7x-(3xy+4y-x)]=4xy+12y+7x-3xy-4y+x=xy+8x+8y=xy+8(x+y)=(-2)+8*3=-2+24=22

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

3x²-xy+y²=101-xy+4y²=421-2得3x²-3y²=6x²-y²=2选B

1/x-1/y=3则x-y=-3xyx-3xy-y/2x-xy-2y=(-3xy-3xy)/(-6xy-xy)=6/7

∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．

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

x^2-3y^2=2xyx^2-2xy-3y^2=0(x-3y)(x+y)=0x=3y或者x=-y当x=3yx+2y=5yx-y=2y所以(x+2y)/(x-y)=5/2当x=-yx+2y=yx-y=

x²-y²=(2-xy)-(1-xy)=1

因为xy/（x+y）=1/2所以x+y=2xy原式=3（x+y)-5xy/(-x-y+3xy)=3*2xy-5xy/(-2xy+3xy)=xy/xy=1

xy/(x+y)=2(x+y)/xy=1/21/x+1/y=1/2(3x-xy+3y)/(-x+3xy-y)=(3/y-1+3/x)/(-1/y+3-1/x)=[3(1/x+1/y)-1]/[(3-(

∵x=2,y=3∴2(xy^2+3y^3-x^2y)-(-2x^2y+y^3+xy^2)-4y^3=2xy²+6y³-2x²y+2x²y-y³-xy&

是不是打错了?应该是x²+y²-3xy吧?（x+y）²=x²+2xy+y²=9①x²+y²-3xy=4②①-②得:x²+