Hello, Greymalkin!

You are expected to know this form of a parabola: .

. . where is the distance from the vertex to the focus.

A spotlight has a parabolic cross section that is 4 ft wide at the opening and 1.5 ft deep at the vertex.

How far is the vertex from the focus?

We have the equation: .Code:| (-2,1.5) | (2,1.5) * - - - - - + - - - - - * | * | * * | * * | * * | * * | * --------------*-------------- |

We are told that when

Hence: .

Therefore: .