To draw a normal line to the mirror, you must draw a line at 90 degrees to the surface of the mirror.
90 Degree Angle - Measurement, Construction, Examples
Geometry - Lines and Angles - Right, acute, and obtuse
Angle of Incidence - Definition, Formula, Diagram, Examples
How to Calculate the Sides and Angles of Triangles Using
Angle of Reflection Definition, Types & Formula - Lesson
angle of reflection
Prove the following. \ If two lines meet to form a right angle
Right Angle - Definition, Shape, Examples and Properties
Brewster Angle - an overview
Right Angled Triangle - Formula, Properties
Perpendicular - Wikipedia
Right Angle - Definition, Properties, Shape, Examples
How to draw a 90 degree angle (right angle) at a point on a line
Normal Line, Definition & Equation - Lesson