Which term describes the imaginary line perpendicular to a boundary, used as a reference in angle measurements?

Which term describes the imaginary line perpendicular to a boundary, used as a reference in angle measurements?

• A. Tangent
• B. Normal
• C. Radius
• D. Altitude

Answer: (B)

A line perpendicular to a boundary used as a reference in angle measurements is called the normal. The normal stands at a right angle to the surface, providing a consistent reference direction for angles, such as the angle of incidence or reflection in optics. The tangent, on the other hand, runs along the boundary, so it is not perpendicular and isn’t used as the standard reference for measuring angles to a surface. The radius is simply a line from the center to the boundary of a circle or sphere, and an altitude is a line from a vertex to the opposite side in a triangle—neither serves as the boundary-perpendicular reference for angles. So the normal is the correct term.

A line perpendicular to a boundary used as a reference in angle measurements is called the normal. The normal stands at a right angle to the surface, providing a consistent reference direction for angles, such as the angle of incidence or reflection in optics. The tangent, on the other hand, runs along the boundary, so it is not perpendicular and isn’t used as the standard reference for measuring angles to a surface. The radius is simply a line from the center to the boundary of a circle or sphere, and an altitude is a line from a vertex to the opposite side in a triangle—neither serves as the boundary-perpendicular reference for angles. So the normal is the correct term.