若f(x,y)=√((xy)+x/y),则f,x(2,1)= 是求f对x的偏导数

f(x+y)=f(x)+f(y)+2xy f(xy,x-y)=x^2+y^2+xy;f(x,y)/∂x;f(x,y)/∂y f(xy)=f(x)+f(y),证明f(x/y)=f(x)-f(y) f(x,y)=xy+e^x x arctanx/y ,求f(x+y,x-y) f(x+y,x-y)=(x^2-y^2)/2xy,求f(x,y)! f(x+y,x-y)=2xy(x-y),求f(x,y) f(xy,x-y)=x^2+3xy+y^2,则f(x,y)=? f(xy,x-y)=x^2-xy+y^2.求f(x,y) 设f(x-y,y/x)=xy,则f(xy,x+y)等于什么 设f(x-y,y/x)=xy,则f(xy,x+y)等于什么 设f(x,y)=xe^y+xy,则f(x+y,x-y)= 任意x,y属于零到正无穷.f（xy）=f（x）+f(y) ,若x>1,f(x) f(x,y)=x*x*x+y*y*y-9xy+27极值 y'=-2xy;求f(x). 设f(x+y,x-y)=x^2+xy,求f(x,y) 设f(x+y,x-y)=xy,z=(xy,x/y),则dz= f(xy,x+y)=(x+y)²-xy,求af(x,y)/ax=? 函数f(xy,x+y)=x^2+xy+y^2,则df(x,y)=?