Since circles don't have sides, what ratio (s) could

you use to prove that all circles are similar?

Radius (ratio of radii)

Step-by-step explanation:

Circles don't have sides, but they all have radii, which are all similar to other circles.

If a triangle has the same relative dimensions as another triangle, we call it similar. Circles always have the same relative dimensions as other circles. You can't pinch or pull the outside of a circle and have it still be a circle.