2.已知 dfrac (x)(x+y)=dfrac (1)(3) ,求 dfrac ({x)^2-(y)^2}(2xy+{y)^2} 的值.

(B) dfrac (x)(y)((y+1))^2-|||-(C) ^2((x+dfrac {1)(x))}^2. (D) dfrac (y)(x)((y+1)

2.设 (xy,x+y)=(x)^2+(y)^2+xy (其中, =xy =x+y), 则 dfrac (partial f)(partial u)+dfrac

6.讨论下列函数的连续性:-|||-(1) (x,y)=dfrac ({x)^2-(y)^2}({x)^2+(y)^2}-|||-(2) (x,y)=dfrac

设=dfrac (2x)({x)^2-(y)^2} ，则 =dfrac (2x)({x)^2-(y)^2}=dfrac (2x)({x)^2-(y)^2}___

求椭球面dfrac ({x)^2}(2)+dfrac ({y)^2}(3)+dfrac ({z)^2}(4)=1上点dfrac ({x)^2}(2)+dfrac

设(X,Y)的分布函数为(x,y)=dfrac (1)({pi )^2}(dfrac (pi )(2)+arctan dfrac (x)(2))(dfrac (

(B) dfrac (1)(2)(X)^2+dfrac (1)(2)(Y)^2 服从x^2分布.-|||-(C) dfrac (1)(3)((X+Y))^2 服

[题目]合并同类项.-|||-(1) (x)^2y-2xy-4x(y)^2+xy+4(x)^2y-3x(y)^2;-|||-(2) dfrac (1)(5)(x

2.作适当的变量变换求解下列方程:-|||-(1) dfrac (dy)(dx)=((x+y))^2 ;-|||-(2) dfrac (dy)(dx)=dfra

已知函数y=y(x)由方程x(y)^2-sin y=0所确定，则dfrac(dy)(dx)=(,,)A、dfrac(cos y-{y)^2}(2xy)B、dfr