Possible Duplicate:
Determine the centre of a circle
My buddy draws a circle then he erase its center. He quiz me how can find the center with only pen and straightedge (no compass).
Do you know how to do that? Or prove that's impossible?
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2$\begingroup$ Circles have centers, but no foci... $\endgroup$– J. M. ain't a mathematicianCommented Aug 23, 2011 at 6:46
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1$\begingroup$ ...anyway, Steiner says, "no". $\endgroup$– J. M. ain't a mathematicianCommented Aug 23, 2011 at 6:49
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$\begingroup$ A vague one- cant u select a point and then sweep the whole circle with this given point pixed and using the other point of the straight edge? i mean u will reach the max distance when its the diameter and its mid point will denote the centre. $\endgroup$– BhargavCommented Aug 23, 2011 at 6:56
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$\begingroup$ @J.M. -- any comments? $\endgroup$– BhargavCommented Aug 23, 2011 at 6:56
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$\begingroup$ @Bhargav: That isn't an allowed use of the straightedge if we follow the rules of the Greeks... $\endgroup$– J. M. ain't a mathematicianCommented Aug 23, 2011 at 6:57
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