Drawing circles
The default method for drawing a circle is to specify a center point and a radius.
Other methods to draw circles can be found in the Circle submenu of the Draw menu and in the Circles toolbar.
The AI_CIRCTAN command draws circles tangent to three linear entities.
The Circle tool is available on:
 The Draw menu.
 The Draw toolbar.
 The Draw ribbon panel.
 The Draw tab of the No Selection Quad.
General procedure

Launch the CIRCLE command.
Prompts you:
Select center of circle or [2 Point/3 Point/TangentTangentRadius/turn Arc into circle/Multiple circles]:

Specify a point.
Prompts you: Set Radius or [Diameter]:

Do one of the following:
 Press Enter to accept the current radius.
 Type a new radius and press Enter.
 Click to define the radius graphically.
Drawing a circle tangent to three entities

Launch the AI_CIRCTAN command.
Prompts you: Enter Tangent spec:

Click a linear entity.
Lines, arcs, circles, polyline segments, xlines and rays are accepted.
Prompts you: Enter second Tangent spec:

Click the second linear entity.
Prompts you: Enter third Tangent spec:

Click the third linear entity.
A circle tangent to the three selected entities is created.
Editing a circle

Select the circle.
The properties of the circle display in the Properties panel.

Type a new value in the Center, Radius, Diameter, Circumference or Area field, then press Enter.

Press the Esc key to stop editing the circle.