To Create a Concentric Arc
1. Click Sketch and then click the arrow next to Arc.
2. Click 
Concentric.
Concentric.3. Select one of the following entities as a reference:
◦ Arc
◦ Arc center point
◦ Circle
◦ Circle center point
A concentric construction circle is created.
4. Drag the construction circle to the desired radius and click to place it.
5. Select the first arc endpoint. The construction circle is removed.
6. Select the second endpoint. The arc is created.