Diameter of a Circle Circumscribed Around a Triangle
Date: 05/13/98 at 05:01:03 From: Eric Subject: Circumscribed Triangle The sides of a triangle are 25, 39, 40. Find the diameter of the circumscribed circle. Please help. I don't even know how to begin, let alone finish it! Thank you very much!
Date: 05/14/98 at 17:43:40 From: Doctor Bob Subject: Re: Circumscribed Triangle Hello Eric, This appears to me to be a tough one! I am going to be very interested in any other ideas about it. I can see a way to get an answer by analytic methods. By this, I mean that we could draw the triangle in a rectangular coordinate system, then determine coordinates for each vertex and for the center of the circle. Place one end of the 40 unit-long side at (0,0) and the other at (40,0). This means the center of the circumscribed circle will be at (20,b). If we can only find b then, the Pythagorean Theorem would carry the day! I suggest that finding the coordinates of the third vertex would be a big help. We should be able to do that since we could assume that this vertex is 25 units from (0,0) and 39 units from (40,0). (Assume the triangle is placed above the x-axis, to keep coordinates positive.) If you are comfortable working with coordinate geometry, the method above will work out. The numbers are even selected so that the algebra works out nicely. I have left out quite a bit of detail that I hope you can supply. Please write back if you need more help with the solution. I would love to see a good synthetic (i.e., coordinate-free) approach. -Doctor Bob, The Math Forum http://mathforum.org/dr.math/
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