Question

the undefined terms line and plane are needed to precisely define which mathematical term?
line segment
perpendicular lines
parallel lines
ray

Explanation:

• Line segment: Defined using two points on a line, no plane needed.
• Perpendicular lines: Defined as lines intersecting at 90° in a plane, but plane is not required for the definition (just two lines).
• Parallel lines: In Euclidean geometry, parallel lines are lines in a plane that do not meet. The definition requires the concept of a plane (to distinguish from skew lines in 3D) and lines. So plane and line are needed.
• Ray: Defined using a point on a line and direction, no plane needed.

Answer:

C. parallel lines