In the figure below, triangle O P N is a reflected image of triangle M P N. Anne states that reflections preserve side lengths, so stack P N with bar on top approximately equal to stack P N with bar on top comma space stack P M with bar on top approximately equal to stack P O with bar on top comma and stack M N with bar on top approximately equal to stack O N with bar on top comma therefore the triangles are congruent. Tim states that reflections preserve angle measures, so angle M P N approximately equal to angle O N P comma space angle M N P approximately equal to angle O P N comma and angle P M N approximately equal to angle P O N comma therefore the triangles are congruent.