Someone asked me this and I can't remember how to work it out!
You have a chord going across a circle (straight line not passing through the middle)
it is 4300units long. At it's centre it is 1175 units away from the nearest edge of the circle.
What's the radius?

I'll try doing a piccy for you if you can't understand me.

 

The problem is to find OD, knowing that AC is 4300 and BD is 1175

 

Hang on, it's a piece of ****. You can work out the angle at BCD using arctan BCD = BD/BC or 1175/2150. That makes BCD 28.66 degrees. That means the other half of it, OCB is (90-28.66)=61.34 degrees. Then you can work out OB as tan 61.34=OB/BC. So OB=3934. That means that OD = 3934+1175 = 5109 (roughly).

The key to it is that the angle OCD is always 90 degrees, as long as C is on the circumference of the circle.

HTH

[Edited by carl - 2/7/2003 3:57:38 PM]

 

Blimey that was quick!! I've just discovered that photoshop is crap for drawing things like this!
Cheers mate!

 

Good old 'paint'