已知函数 =(x)^3y+3(x)^2(y)^2-x(y)^3 ,则 =(x)^3y+3(x)^2(y)^2-x(y)^3 ( ) A =(x)^3y+3(x)^2(y)^2-x(y)^3 B =(x)^3y+3(x)^2(y)^2-x(y)^3C =(x)^3y+3(x)^2(y)^2-x(y)^3 D=(x)^3y+3(x)^2(y)^2-x(y)^3

A (x,y)=(x)^3-6(x)^2y-3x(y)^2+2(y)^3 . B (x,y)=(x)^3-6(x)^2y-3x(y)^2+2(y)^3 . C

以下函数数中,是(x,y)=(x)^3-3x(y)^2-y的共轭调和函数的是(x,y)=(x)^3-3x(y)^2-y (x,y)=(x)^3-3x(y)^2-

1.计算:(3x+y+2)(3x-y-2).2.已知(3x+y+2)(3x-y-2).求（a+b-c）²。3.设x>0,且(3x+y+2)(3x-y-2).求(

10.已知线性变换-|||- ) (x)_(1)=2(y)_(1)+2(y)_(2)+(y)_(3) (x)_(2)=3(y)_(1)+(y)_(2)+5(y

3.已知两个线性变换-|||- ) (x)_(1)=2(y)_(1)+(y)_(3), (x)_(2)=-2(y)_(1)+3(y)_(2)+2(y)_(3)

设函数(x,y,z)=2(x)^3y-3(y)^2z在点(x,y,z)=2(x)^3y-3(y)^2z处梯度的模为(x,y,z)=2(x)^3y-3(y)^2z

(7) dfrac (dy)(dx)=dfrac (2{x)^3+3x(y)^2+x}(3{x)^2y+2(y)^3-y}

15.求下列函数的极值.-|||-(1) (x,y)=(x)^3-4(x)^2+2xy-(y)^2+3 ;-|||-(2) (x,y)=3xy-(x)^3-(y

3.已知两个线性变换-|||- ) (x)_(1)=2(y)_(1)+ (y)_(3) (x)_(2)=-2(y)_(1)+3(y)_(2)+2(y)_(3

(x,y,z)=(x)^3+4(y)^3+4(z)^2，则(x,y,z)=(x)^3+4(y)^3+4(z)^2（）。(x,y,z)=(x)^3+4(y)^3+