# Math Help - Parabolic equation of a bridge

1. ## Parabolic equation of a bridge

Just want to make sure I'm on the right track.

I'm using $y=ax^2$ where a<0 for the bridge.

Data (arbitrary units):
Height 90
Length 500

$90=a(\frac{500}{2})^2$

$-a=0.00144$

$\therefore y=-(0.00144)x^2$

Or is there a better way of doing this?

2. Your answer is correct.