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6x 2 xy 2y 2 2x 8y 8

原式=3x(2x-y-2)+3xy+6x+xy-2y2+2x-8y-8=3x(2x-y-2)+4xy-2y2+8x-8y-8=3x(2x-y-2)+2y(2x-y-2)+2y2+4y-2y2+8x-8y-8=3x(2x-y-2)+2y(2x-y-2)+8x-4y-8=3x(2x-y-2)+2y(2x-y-2)+4(2x-y-2)=(2x-y-2)(3x+2y+4)

令x-1=s,y+2=t,即x=1+s ,y=t-2,代入得 f(x,y)=4(1+s)^2+(1+s)(t-2)-(t-2)^2-6(1+s)-3(t-2)+5打开化简得 =4s^2-t^2+st+2t+3=3+2t+4s^2+st-t^2。 f(x,y)=e^xln(1+y)=(1+x+x^2/2+x^3/3+....)(y-y^2/2+y^3/3+....) =y+xy-y^2...

6x??-5xy+y??=0 (2x-y)(3x-y)=0 2x-y=0或3x-y=0 即2x=y或3x=y 当2x=y代入x??+xy+y??=7 得x??+2x??+4x??=7 7x??=7 x??=1 x=±1 y=2x=±2 当y=3x代入x??+xy+y??=7 得x??+3x??+9x??=9 13x??=9 x??=13分之9 x=±13分之3√13 y=3x=±13分之9√13 即x=1...

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

设2x+y=m 把y=m-2x代入4x^2+y^2+xy=1整理得:6x^2-3mx+m^2-1=0 △=9m^2-24(m^2-1)>=0 -2√10/5=<=m<=2√10/5 所以2x+y的最大值是:2√10/5

原式= -2x²-2xy-4x²+2xy-2y² =-6x²-2y² =-2(3x²+y²) 因为只有x=y=0时 才有3x²+y²=0 所以xy≠0则3x²+y²>0 所以-2(3x²+y²)

(1)x2y-xy2=xy(x-y);(2)3x2+6x+3=3(x2+2x+1)=3(x+1)2.故答案为:xy(x-y),3(x+1)2.

A-B=(5m+1)x2+(3n-2)xy-3x+y-(6x2-5mxy-2x-1)=(5m+1)x2+(3n-2)xy-3x+y-6x2+5mxy+2x+1=(5m-5)x2+(5m+3n-2)xy-x+y+1,已知A和B的差不含二次项,∴5m-5=0,5m+3n-2=0,得:m=1,n=-1,∴(-1)m-n[-m+n-(-n)3m]=(-1)1-(-1)×[-1+...

(2x-3y+b)(3x+y+c) =(2x-3y)(3x+y)+b(3x+y)+c(2x-3y)+bc =6x^2-7xy-3y^2+(3b+2c)x+(b-3c)y+bc ∵6x^2-7xy-3y^2+14x+y+a=(2x-3y+b)(3x+y+c) 14=3b+2c 1=b-3c a=bc ∴a=4 b=4 c=1

-xy(9x^2y+6xy-3)

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