January 19, 2017

Homework Help: Math: Distance and Midpoint

Posted by Anonymous on Tuesday, April 24, 2012 at 6:05pm.

Three points on the edge of a circle are (-220, 220), (0, 0), and (200, 40), where each unit represents 1 foot. What is the diameter of the circle to the nearest 10 feet?

I know the answer is supposed to be 550 ft, but I keep coming up with the wrong answer. I found the midpoint of (-220, 220) and (0, 0) which is (-110, 110). Its perpendicular bisector is y = (1/2)x +165, if I did it correctly. I also found the midpoint of (0, 0) and (200, 40), which is (100, 20). I got y = -5x + 520 for its perpendicular bisect. Using those two equations, I found the intersect/center of the circle, (710/11, 2170/11). But when I use the distance formula with that point and (0, 0) to find the distance/radius, I get about 207.5, and the diameter about 415. What did I do wrong?

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