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

The combined equation of the tangent and normal to the curve $x y=15$ at the point $(5,3)$ is________

The length and breadth of a rectangle are $x_{x \mathrm{~cm}}$ and $y \mathrm{~cm}$ respectively. If the length decreases at the rate of $5 \mathrm{~cm} /$ minute and the breadth increases at the rate of $3 \mathrm{~cm} /$ minute, then the rates of change of the perimeter and area respectively when the length is 5 cm and breadth is 2 cm , are