若函数f(x,y)=x^2-xy+y^2在点（1,1）处沿与x轴正方向夹角为α的方向上的方向导数取最大值,则α=?我要考试了

函数f(xy,x+y)=x^2+xy+y^2,则df(x,y)=? 设函数f(xy,x+y)=x^2+y^2+xy,求∂f(x,y)／∂x和∂f(x,y)／∂y 函数f(xy,y^2/x)=x^2+y^2,求f(y^2/x,xy) 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 函数f(x,y)=xy/x*2 y*2,求limf(x,y)与limf(x,y) 设函数f(x,y)=xy/根号x^2+y^2,求limf(x,y)x,y趋于0 f(x)满足f(x+y)+f(xy)=2f(x)f(y)求函数的奇偶性 求函数f(x,y)=x^2-xy+y-3x的极值 函数y=f(x)对任意实数x,y都有f(x+y)=f(x)+f(y)+2xy 求f(0)的值 设函数f(x,y)=(2xy)除以（x^2+y^2)求f（1,y/x) 求函数的表达式已知f(x,y)=xy/(x^2+y^2)则f(y/x,1)=? f(x+y,x-y)=(x^2-y^2)/2xy,求f(x,y)! 多元函数概念习题 f（xy,x/y)=(x+y)^2 ,则f（x,y)=? 二元函数问题,求f(x,y) 1.f(x+y,x-y)=2(x^2+y^2)e^(x^2-y^2) 2.f(x+y,xy)=2x^2+xy+2y^2 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)