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Radius of a circle

  1. Jan 15, 2006 #1
    I'm trying to calculate the radius of the circle [tex]x^2 - 2ax + y^2 - 2ay = 0[/tex]
    I completed the square and got to [tex](x-a)^2 + (y-a)^2 = 2{a}^2[/tex]
    That would mean the radius is [tex]\sqrt{2{a}^2}[/tex] right? Which would be [tex]\sqrt{2}\sqrt{a^2} \Rightarrow a\sqrt{2}[/tex]... but my textbook quotes the answer as [tex]\sqrt{2a}[/tex] :confused: Did I do something wrong or is my textbook incorrect?
  2. jcsd
  3. Jan 15, 2006 #2


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    Your textbook is wrong.
  4. Jan 16, 2006 #3


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    Are you sure you are reading your textbook? It might be that the answer is [itex]\sqrt{2}a[/tex] but a little blurred so it is not clear where the square root sign ends- it looks like [itex]\sqrt{2a}[/itex].

    On the otherhand that is exactly why most texts would use the clearer [itex]a\sqrt{2}[/itex] as you do.
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