Inscribe Square in Circle using Compasses Alone/Corollary

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To inscribe a regular dodecagon in a given circle,
by means of compass alone,
supposing the center to be known.


We use the same construction as for Inscribe Square in Circle using Compasses Alone:


Then we note that, for example, $C$ and $E$ are $30 \degrees$ apart.

Hence they are adjacent vertices of a regular dodecagon inscribed in the circle.

It remains to construct the remaining vertices, which is done by, for example, setting the compass to $CE$ and drawing an arc with center $C$ and working round the circle.