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Given three NSPoint (Or points on a plane), how to find the radius or the center point. Given P1 (a,b), P2 (c,d), P3 (e,f)

How would you calculate this, I need this for my UIBezierPath drawing. I am currently looking through wikipedia and other website, but failed to understand it fully. How would you calculate the radius?

Where radius is at (X,Y)

What is X, Y

31i45
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  • are the three points on the circle whose radius you wish to find? If not, there is no unique solution. For example, if the points were all on the same line, how would you define the radius? –  Feb 22 '16 at 04:01
  • No three Point are on a line. Meaning, you can not draw a line through the three points. How would you find the radius? – 31i45 Feb 22 '16 at 04:11
  • Assume those 3 points form a trinagle [keep reading](https://en.wikipedia.org/wiki/Triangle_center) – 4oby Feb 22 '16 at 05:28
  • None of you are answering the question, how do i find the radius? – 31i45 Feb 22 '16 at 05:35
  • The radius of what? Only circles have a radius. So are the three points on the circumference of a circle? –  Feb 22 '16 at 07:08
  • Micheal, are you not familiar with the concept that any three points can go through a circle. "Through any three points, not all on the same line, there lies a unique circle." - https://en.wikipedia.org/wiki/Circle. That means, there is a radius. A line from three points that is of the same length and meet at a point (Centre). – 31i45 Feb 22 '16 at 10:04
  • Well you did not say that your points were not on the same line. So see my answer below: it answers your original question as long as the points are not on the same line. –  Feb 24 '16 at 04:03
  • You can still draw a circle through 3 point which are on a straight line. Just a very... big circle. – 31i45 Feb 24 '16 at 05:35
  • Yes with an infinite radius. I agree. Well there you go. I hope the link I pointed you to helps you. Good luck. –  Feb 24 '16 at 16:10

1 Answers1

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See this answer. I am assuming that the three points are points on the circle whose radius you wish to find.

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