$\"\"$

The distance from vertex to focus is $\"\"$ and depth is $\"\"$ .

Set the vertex of the parabola is at $\"\"$ and it opens up.

The general form of the parabola is $\"\"$ , where $\"\"$ is distance from vertex to focus.

Thus the value of $\"\"$ and the points on the parabola are $\"\"$ and $\"\"$ .

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

$\"\"$

Where $\"\"$ is the diameter of the headlight.

Therefore, the diameter of the headlight is $\"\"$ .

$\"\"$

The diameter of the headlight is $\"\"$ .