Each ray starting from [math]y=8[/math] will travel, hit the parabola at some point [math]P[/math] and reflect to [math]F[/math]. The distance traveled equals the sum of the distance from [math]y=8[/math] to [math]P[/math] and [math]PF[/math]. Because, by the definition of a parabola, [math]PF=PD[/math], we have that the distance traveled is the same as the distance from [math]y=8[/math] to the directrix, no matter where we started. This distance will just be [math]8+p[/math].[br]This means the 10 rays starting at the different points will all travel the same distance by the time they reach [math]F[/math]. If they are moving at the same speed, they will arrive simultaneously. Animate the diagram to see this happen.