$\mathrm{f}(x)=\frac{x}{2}+\frac{2}{x}, x \neq 0$ is strictly decreasing in

The rate of change of the volume of a sphere with respect to its surface area, when the radius is 5 m is

If the line $a x+b y+c=0$ is normal to the curve $x y=1$, then

The sum of two nonzero numbers is 4 . The minimum value of the sum of their reciprocals is