A circle is always similar to another circle, because we can always map one onto the other using only dilations and rigid transformations.
Explanation:
Two Circles are said to be similar if all the linear measurements of the circles are proportional.
Lets consider if two circles have a certain ratio of their radii, , it definitely mean that all the other corresponding ratios will also have that same ratio.
Concentric circles are defined as the circles which have a common center. The area between the two concentric circles having difference in their radii is Known as annulus.
The most important property of a circle is that all points on the circle are equidistant (i.e. having the same distance) from the center point.
A circle is always similar to another circle, because we can always map one onto the other using only dilations and rigid transformations.