Answer:
128
Step-by-step explanation:
I assume there's a negative sign missing, since the image is a downwards parabola.
f(x) = -x²/256 + 16
The width of the beam is the distance between the x-intercepts.
0 = -x²/256 + 16
x²/256 = 16
x² = 4096
x = ±64
So the width is:
64 − (-64) = 128
