I've been trying to find the answer to this but haven't come up with it and I'm almost positive it is out there. So, I come to harvest the motliest crue of minds ever assembled - TB! Here's my question. From the diagram below - if the length of the cord AB is known and the "height" of the arc - shown as CD is known, is there a formula to calculate the diameter or radius of the circle they inhabit? And can we get this done without pulling out the sine tables? Thanx in advance for your help.