Hello, magentarita!
A searchlight is shaped like a paraboloid of revolution.
The light source is located 2 feet from the base along the axis of symmetry
and the depth of the searchlight is 4 feet.
What should the width of the opening be? Code:
4
*      +      *

*  *
* 2* *
*  *
*  *
       *       

We are expected to know this equation: .
. . where is the distance from the focus to the vertex.
Since , the equation is: .
When
Therefore, the width of the opening is feet.