The maximum value of $$f(x)=\frac{x}{1+4 x+x^2}$$ is

The minimum value of $$f(x)=x+\frac{4}{x+2}$$ is

The condition that $$f(x)=a x^3+b x^2+c x+d$$ has no extreme value is

At any point $$(x, y)$$ on a curve if the length of the subnormal is $$(x-1)$$ and the curve passes through $$(1,2)$$, then the curve is a conic. A vertex of the curve is