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If I know the coordinates of the center and one vertex of an equilateral triangle, how do I find the coordinates of the other vertices?

I'm thinking I need to find (x,y) such that the distance to the known vertex is the square root of 3 times the distance to the center, so just need to solve those two distance equations simultaneously, but I keep coming up with too many unknowns.

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    By compass and straightedge construction this is quite easy, so keep perservering (there are not too many unknowns).2012-11-18
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    If you want to do it via coordinate geometry, the easiest way I can think of is to take a reference equilateral triangle with center at $(0,0)$ and vertices at $(\cos 2n\pi/3, \sin 2n\pi/3)$ and transform it to match your triangle.2012-11-18
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    Thanks to everyone for all the solutions!2012-11-19

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