若x y=6,xy=5,x-y

(x+y)"=(x-y)"+4xy=25+24=49x+y=±7x"y+xy"=xy(x+y)=±42

Solution:x^2-2xy+3y^2=9(1)4x^2-5xy+6y^2=30(2)Eq(1)*5-Eq(2)*2,wehavex^2-y^2=5(3)Eq(2)-Eq(1),wegetx^2+

5xy+4x+7y+6x-3xy-4xy+3y=5xy-3xy-4xy+4x+6x+7y+3y=（5-3-4）xy+（4+6）x+（7+3）y=-2xy+10x+10y=-2xy+10（x+y）因为x

首先化简：原式=7x+4y+xy-5y-6x+6xy=(x-y)+7xy因为,x-y=5,-xy=3所以原式=5-21=-16楼上忘记加负号了~

你好：原式=（7x+4y+xy)-(5y+6x-6xy)……………………把“6”乘进去=7x+4y+xy-5y-6x+6xy=x-y+7xy因为x-y=5,-xy=3所以xy=-3所以,原式=5+7乘

x=-1,y=-6或x=6,y=1代入式子得x^2-xy^2=37或30x^2y+xy^2=-42或42

2x+y+6=xy化简得：Y=(2X+6)/(X-1)X不等于0因为正实数x.所以X>0所以X>1函数Y=(2X+6)/(X-1)是单调递增所以X=2为最小值,Y=10所以XY最小值为XY=20

先把代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)化简（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)=5XY+4X+7Y+6X-3XY-4XY+3Y=-2XY+10X+1

第1小题：x²y-xy²=xy(x-y)=6(5)=30第2小题：(x+y)²=x²+y²+2xy=x²+y²-2xy+4xy=(

（7xy+4x-7y）+(6x-3xy)-(3y+4xy)=7xy+4x-7y+6x-3xy-3y-4xy=10x-10y=10（x-y）=10*3=30

(5xy+4x+7y)+(6x-3xy)-(4xy-3y)=5xy+4x+7y+6x-3xy-4xy+3y=(5xy-3xy-4xy)+(4x+6x)+(7y+3y)=-2xy+10x+10y=-2x

（7x+4y+xy）-6（5/6y+x-xy）=7x+4y+xy-5y-6x+6xy=x-y+7xy=5+7×(-3)=-16

把括号打开7X+4Y+XY-5Y-6X+6XY=X-Y+7XY=5+7*(-3)=-16

(7x+4y+xy)-6(六分之五y+x-xy)=7x+4y+xy-5y-6x+6xy=x-y+10xy把x-y=5和-xy=3代入x-y+10xy=5+10*(-3)=5-30=-25所以原式的值是

(x+y)²=x²+2xy+y²=(x²-2xy+y²)+4xy=(x-y)²+4xy=49所以x+y=±7x²y+xy²

解x²y-xy²=xy(x-y)=5×1=5a²b+ab²=1∴ab(a+b)=1∵a+b=3∴3ab=1∴ab=1/3再问：a(a-b)-a+b=?再答：=a

X+y=3xy=-5X-y=?(x-y)^2=(X+y)^2-4xy=9+20=29则x-y=±根号29

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

x^2y+xy^2＝xy×（x+y）＝6×5＝30

因为,x-y=3xy所以：-3x+6xy+3y/[(7x-5y)-9xy-(3x-y)]=[-3(x-y)+6xy]/[(7x-5y)-9xy-(3x-y)]=[-3*3xy+6xy]/[7x-5y-