Question

which undefined term is used to define an angle?
line
plane
point
ray

Explanation:

An angle is defined as the union of two non - collinear rays with a common endpoint. Among the given options, the ray is the undefined term used in this definition. A line is a straight path with no endpoints, a plane is a flat surface, and a point is a location. But for an angle, the key undefined term is the ray.

Answer:

ray