If $x$ and $y$ are sides of two squares such that $y=x-x^2$, then the rate of change of area of the second square with respect to that of the first square is

The function $\mathrm{f}(x)=[x(x-2)]^2$ is increasing in the set

The minimum value of $a x+b y$ where $x y=c^2$ is

The equation of the tangent to the curve $y=\mathrm{be}^{-x / \mathrm{a}}$ at the point where it crosses the Y axis is