Question

which defines a circle?
two rays with a common endpoint
a piece of a line with two endpoints
a piece of a line with one endpoint
all coplanar points equidistant from a given point

Explanation:

• A circle is defined as the set of all coplanar points that are equidistant from a given point (the center).
• Two rays with a common endpoint define an angle.
• A piece of a line with two endpoints is a line segment.
• A piece of a line with one endpoint is a ray.

Answer:

all coplanar points equidistant from a given point