1.函数 (x+y,xy)=(x)^2+(y)^2-xy, 则 f(x,y)=

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

5【判断题】设f(x,y)=(xy)/(x^2)+y，则f(xy,(x)/(y))=(xy)/(xy^3)+1.A. 对B. 错

已知x，y都是正数，且x≠y，求证：（1）(x)/(y)+(y)/(x)＞2；（2）(2xy)/(x+y)＜sqrt(xy)．已知x，y都是正数，且x≠y，求证

设 (x,y)=dfrac ({x)^2+(y)^2}({e)^xy+xysqrt ({x)^2+(y)^2}} ,则 (f)_(x)(1,0)= __ _.

1.讨论下列函数的连续性:-|||-(1) (x,y)=tan ((x)^2+(y)^2) ;-|||-(2) (x,y)=[ x+y] ;-|||-(3)

设 =(e)^xy+ln ((x)^2+(y)^2) 则（ ）A =(e)^xy+ln ((x)^2+(y)^2)B =(e)^xy+ln ((x)^2+(y)

5.(单选题) 设f(x,y)=(x+y)/(xy),则f(x+y,x-y)=（）A. $\frac{2x}{y^{2}-x^{2}}$B. $\frac{2x

微分方程x^2y`+xy= y^2, y|x=1=1 的特解为A x^2y`+xy= y^2, y|x=1=1 B x^2y`+xy= y^2, y|x=1=1

[单选题]已知函数的全微分df(x,y)=(3x2+4xy-y2+1)dx+(2x2-2xy+3y2-1)dy，则f(x,y)等于（　　）.A.B.C.D.

[单选题]已知函数的全微分df(x,y)=(3x2+4xy-y2+1)dx+(2x2-2xy+3y2-1)dy，则f(x,y)等于（　　）.A.B.C.D.