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 angle between the line $x=\frac{y-1}{2}=\frac{z-3}{\lambda}$ and the plane $x+2 y+3 z=6$ is $\cos ^{-1} \sqrt{\frac{5}{14}}$, then the value of $\lambda$ is