求f(x,y)=x^2+xy+y^2 的极值.不要求二阶偏导吗？

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-xy+y^2.求f(x,y) y'=-2xy;求f(x). 求f(x,y)=xy-x^2-y^2+2x+2y的极值? 求 f(x,y)=x^4+y^4-x^2-y^2-xy的极值! 求f(x,y)=x^2+xy+y^2+x-y+1的极值 f(x^2-y^2,x-y)=x+y+x^2-xy,求fy(x,y)的导数. 设f(x+y,x-y)=x^2+xy,求f(x,y) f(x^2-y^2,x-y)=x+y+x^2-xy,求f'(x,y)对y求导 f(x)满足f(x+y)+f(xy)=2f(x)f(y)求函数的奇偶性 对任意的实数x,y,f(x+y)=2f(y)+x^2+2xy-y^2+3x-3y,求f(x) f(2x+y,2y+x)=xy,求f(x,y) 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 f(x+y)=f(x)+f(y)+2xy y'=-2xy;求f(x).y'=2y/x+2;求y 已知二元函数f(xy,x+y)=x^2+y^2,求f(x,y) 请阐明一下与这个式子在解法上的不同之处f(x+y,xy)=x²+y²，求f(x,y)