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Homework Help: Complex Numbers Circle Equation

  1. Jan 15, 2012 #1


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    1. The problem statement, all variables and given/known data

    Write the equation of a circle in complex number notation: The circle through 1, i, and 0.

    2. Relevant equations

    3. The attempt at a solution

    I know the equation for a circle with complex numbers is of the form |z-a| = r where a is the center point and r is the radius. I don't know how I'd go about finding it where they only give you 3 points like this. I assume the points correspond to complex numbers like w = x + iy == (x,y) so they'd be (1,0) (0,1) and (0,0)? I'm not sure where to go next and any help would be appreciated! thanks!
  2. jcsd
  3. Jan 15, 2012 #2


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    Yes, think of the points (1,0), (0,1) and (0,0). Think of doing some geometry to find the center. E.g. the perpendicular bisector of each segment connecting two of those points goes through the center, right?
  4. Jan 15, 2012 #3


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    ok, so then would the center be at (1/2, 1/2)?
  5. Jan 15, 2012 #4


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    ok, I figured it out. Geometrically I found the center to be (1/2, 1/2) and then used that to find the radius from that point to a different point, (0,0), since that's easy to do then did sqrt((1/2)^2+(1/2)^2) to find the length of it which came out to 1/sqrt(2) so then the equation is just |z-(1/2)(1+i)| = 1/sqrt(2). Thanks for your help!
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