



 
Hi Jennifer, I added some lines and labels to the diagram you sent> In particular $C$ is the centre of the circle. Also from your diagram $d$ is not the diameter of the circle but the length of the chord where he circle intersects the Xaxis. Triangle $ABC$ is a right triangle so by ythagoras Theorem \[ r^2 = (r  x)^2 + \left( \frac{d}{2}\right)^2 .\] From the diagram \[2r  x = 500.\] Solve theis equation for $x,$ substitute into the first equation and solve for $r.$ Penny  


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