#Circle

Key C. The ways to define it are switched in the top bar.

• Centre and radius — the usual way.
• By two points — they set the diameter.
• By three points — a circle through three given points.
• Tangent — a circle touching the chosen line.

#The radius is held by constraints

Tangency, equal radii and point-on-circle are full constraints: move a neighbour and the circle rebuilds after it. A circle boxed in by tangencies can be fully defined without a dimension at all.

#What next

A closed circle is a ready profile: extrude it into a cylinder or cut a hole with it. For holes in a body the Hole command is usually better: it keeps a reference to the face and survives a rebuild.