To find the center of a given circle. * Let $ABC$ be the given circle. * So it is required to find the center of circle $ABC$. * Let some straight line $AB$ have been drawn through ($ABC$), at random, and let ($AB$) have been cut in half at point $D$ [Prop. 1.9]. * And let $DC$ have been drawn from $D$, at right angles to $AB$ [Prop. 1.11]. * And let ($CD$) have been drawn through to $E$. * And let $CE$ have been cut in half at $F$ [Prop. 1.9]. * I say that (point) $F$ is the center of the [circle] $ABC$.
It is possible to locate the center of a circle.
Proofs: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Propositions: 29 30 31
Sections: 32