The most economical proportion of the height of a covered box of fixed volume whose base is a rectangle with one side three times as long as the other, is

The slope of the tangent to the curve, $$y=x^2-x y$$ at $$\left(1, \frac{1}{2}\right)$$ is

Let $$f(x)=a+(x-4)^{\frac{4}{9}}$$, then minima of $$f(x)$$ is

The function $$f(x)=\frac{x}{2}+\frac{2}{x}$$ has a local minimum at