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Incribing a Pentagon in a Circle

Date: 2/6/96 at 16:43:28
From: Anonymous
Subject: Inscribing a pentagon in a circle

I'm stuck trying to inscribe a pentagon. I can easily inscribe a
square by just drawing to perpendicular diagonals. I also know
that 360/5 = 72 but that doesn't help me at all.
Can you help?

Thanks a googol.

Date: 3/10/96 at 0:18:54
From: Doctor Jodi
Subject: Re: Inscribing a pentagon in a circle

Wow Evan, I can't believe that you're thanking us a googol! (I just
found out what that is, actually.... !)

First of all, to inscribe any old pentagon in a circle, just drawing it
should be easy enough.

But if you want to draw a REGULAR pentagon, then it helps to know that
each angle needs 72 degrees.  Now you need to find a protractor and draw
a line at 72 degrees from any one point on the circle to another.  Now
do the same thing starting with one of those two endpoints, etc., and
continue until you get a regular pentagon.

Let me know if this works.

(On the other hand, you could draw a regular pentagon using a protractor
and then draw a circle touching each of its 5 endpoints. But that would
be too easy - don't you think?)

-Doctor Jodi,  The Math Forum
Associated Topics:
High School Conic Sections/Circles
High School Geometry
High School Triangles and Other Polygons

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