And a circle is said to be circumscribed about a rectilinear (figure) when the circumference of the circle touches each angle of the (rectilinear) figure about which it is circumscribed.
If a rectilinear figure is inscribed in the circle, then the circle is said to be circumscribed about the figure.
The pentagon is inscribed in a circle and the circle is circumscribed about the pentagon:
Proofs: 2 3 4 5 6 7 8 9 10
Propositions: 11 12 13