记F(x,y)=x+y-a(x+2*(2xy)^0.5,x,y为正实数,若对任意x,y恒有F(x,y)大于等于零,求a的范围?

f(x+y,x-y)=(x^2-y^2)/2xy,求f(x,y)! 设f(x+y,x-y)=x^2-y^2,则f(x,y)= 若f(x+y,y/x)=x^2-y^2,则F(X,Y)= 已知f(x+y,y/x)=x^2-y^2,则f(x,y)= f(x+y,y/x)=x^2-y^2求f(x,y) f(x+y,y/x)=x^2-y^2,求f(x,y),详见里面 f(x+y,x-y)=2xy(x-y),求f(x,y) 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 设f(x)=(a^x+a^y) (a>0),证明f(x+y)+f(x-y)=2f(x)f(y)设f(x)=(a^x+a^-x) (a>0),证明f(x+y)+f(x-y)=2f(x)f(y) (X,Y) f(x,y)={12y^2,0 f(x+Y)+f(x-y)=2f(x)f(Y) 求其是偶函数 急 求证f（x+y）+f(x-y)=2f(x)f(y)是周期函数 f(x^2-y^2,x-y)=x+y+x^2-xy,求f'(x,y)对y求导 已知F(X+Y,X-Y)=X^2*Y+X*Y^2,则F(X,Y)=? 设f(x+y,x-y)=x^2+y^2-x*y求f(x,y) f(x+y)+f(x-y)=2f(x)cosy,求证f(x)为周期函数 f[(x+y)/2]