The relation q is described as a list of ordered pairs, shown below.

q = { (-2, 4), (0, 2), (-1, 3), (4, -2) }

domain:
range:

Domain : {-2, -1, 0, 4}

Range: {-2, 2, 3, 4}

The cross-section of the beam with  a parabola will more or less look like the one below, check picture below

now, if we take the 3 to be the focus point, and we put the parabola at the origin, like the second picture below

then we can do something like