Equation of a Circle with Three Points: Guide and Explanation

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Discussion Overview

The discussion revolves around the possibility of finding the equation of a circle given three points in a two-dimensional space. Participants explore the conditions under which this is feasible, including the geometric implications of the points' arrangement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about the feasibility of determining a circle's equation from three points.
  • Another participant suggests that all points should satisfy the equation xi^2 + yi^2 = r^2, indicating a method to construct equations to find the radius.
  • It is asserted by a participant that three non-collinear points uniquely specify a circle.
  • A further explanation is provided on finding the center of the circle by determining a point equidistant from all three points, referencing a method involving perpendicular bisectors of segments between pairs of points.
  • A participant concludes with a proof statement about non-collinear points determining a unique circumscribed circle around a triangle.

Areas of Agreement / Disagreement

Participants generally agree that it is possible to find the equation of a circle from three non-collinear points, though the methods and explanations vary. No significant disagreements are noted, but the discussion includes different approaches to the problem.

Contextual Notes

The discussion assumes that the three points are non-collinear, which is a critical condition for the uniqueness of the circle. The mathematical steps and specific methods for deriving the circle's equation are not fully resolved.

abia ubong
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hi,
my friend once asked me if i could find the equation of a circle,when given three points,i mean (x,y) (x2,y2) (x3,y3).please let me know if it is possible.
 
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I think you can. All pairs (xi,yi) should fullfill xi^2+yi^2=r^2 where r is the radius. You should be able to construct a linear set of equations and solve for r.
 
Yes it is possible. Three points will always uniquely specify a circle providing that they are not co-linear.
 
It definitely is possible. What you're doing is finding a point that is equidistant from all three points and that will give you the centre of the circle. Then the radius is just the distance from the centre to any point. If you ever watch cop shows and they are talking about triangulating a radio signal from 3 points this is what they are referring to (sort of).

So how do you do it? It's actually really easy when you think of it this way. If you take two random points and graph the points that are equidistant from both you get a line. Specifically a line that intersects the line segment between the two points at 90 degrees at the half way point. Just pick two pairs of points (one point will be in both pairs). Draw the equidistant lines for both pairs. The intersection point is the point of equidistance from all 3. Hence it is the centre of the circle.
 
thanks a lot
 
Proof:3 noncolinear points determine a nondegenerate triangle uniquely.Any nondegerate triangle has a circumscribed circle.EndProof.

Daniel.
 

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