In geometry, 2 or more objects are said to be concentric, coaxial, or coaxal when they share the same axis or center.

Circles, regular polygons, regular polyhedra, spheres, and cylinders may be concentric to one another (sharing the same center point).

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## Definition of Concentric Circles

Concentric Circles are 2 or more circles which have same center point.

They fit inside each other and are the same distance apart all the way around.

### Example

- c = center point
- r
_{1 }= radius of small circle - r
_{2 }= radius of large circle

The region between two concentric circles is called an annulus.

## Concentric Circles in Real World

Concentric circles are also found in diopter sights (commonly found on target rifles). They feature a large disk with a small diameter hole near the shooter’s eye, and a front globe sight. When these sights are correctly aligned, the point of impact will be in the middle of the front sight circle.