The amount of illumination $A$ from a light source is inversely proportional to the square of the distance $d$ from the source.  

1. Express $A$ as a function of $d$.

   Answer (a):

   $A(d)=\frac{k}{d^2}$

2. If the distance from a light source is tripled, what happens to the amount of illumination?

   Step (b):

   $A(3d)=\frac{k}{(3d)^2}$