Question

2. Explain why the phrase "on a plane" is included in the definition of a circle. What would be defined if the phrase were not included ?

Answer 1

because the definition your looking at is probably "All points on a plane that are equally distant from a common point (center)."

If the "all points" was excluded, then it will be describing a sphere.

Answer 2

Actually, the "all points" is in both the definition of a sphere and a circle. The key words that make it different are "in a plane."

Answer 3

sorry, I meant "on a plane"