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Reflections

Opposite Isometries

Any isometry that reverses the orientation of a triangle is called an opposite isometry.  When you read off the vertices of triangle ABC in cyclic order, they are read in a counterclockwise direction. When you read off the vertices of triangle A'B'C' in cyclic order, they are read in a clockwise direction.
 is the notation we will use for a reflection in line m.   In the sketch below, we would write .

Reflection