# Plot circles using the various historical approximations of Pi?

Posted 3 months ago
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 I want to be able to see the over or under approximations as a consequence of using older approximations of Pi such as 355/113 or 25/8 instead of the default value used by Mathematica. I was not able to see any visible difference by using the ReplaceAll function to replace Pi. What kind of function can I use to to plot a circle to demonstrate these differences to students?Thank you! Attachments: Answer
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Posted 3 months ago
 (1) The Wolfram Language is case-sensitive. So Pi is not the same as pi.(2) A Circle primitive is going to be a graphic of a circle. No substitution will change that.(3) It is quite unclear, both from post and notebook, what exactly is the goal. A circle is a circle, independent of how ratio of circumference to diameter is evaluated. Answer
Posted 3 months ago
 Thank you for your response, Daniel.Do I understand correctly that you are saying Pi plays no role in the plotting of a circle? If this is true, I'd like to know how they are plotted. Answer
Posted 3 months ago
 I am not privy to how Mathematica does things under the hood, but it is indeed true that one does not need $\pi$ to draw a circle. On the conceptually simpler end of things, there is e.g. Minsky's method, whose (naive) Mathematica implementation might go like With[{h = N[1/16]}, Graphics[Line[NestList[{{1, -h}, {h, 1 - h^2}}.# &, {1, 0}, Round[8/h]]]]] and on the fancier end of things, one can use non-uniform rational B-splines (NURBS), which is mathematically equivalent to parametrizing a circle with the stereographic projection: With[{n = 150}, ParametricPlot[{1 - u^2, 2 u}/(1 + u^2), {u, -n, n}, PlotRange -> All]] Jim Blinn gives a good survey of various methods here. All of this is independent of computing $\pi$. Answer
Posted 3 months ago
 Thank you for your reply, JM. If π is not necessary to draw a circle, I will rephrase my question: What can I plot to demonstrate the consequences of using different approximations of π? Answer