Reflection Rules

A geometric reflection flips a shape over a line of reflection. The coordinates of any reflected point are determined by these standard transformation rules:

  • Reflection across the x-axis: (x,y)ightarrow(x,y)(x, y) ightarrow (x, -y)
  • Reflection across the y-axis: (x,y)ightarrow(x,y)(x, y) ightarrow (-x, y)
  • Reflection across the line y=xy = x: (x,y)ightarrow(y,x)(x, y) ightarrow (y, x)
  • Reflection across the line y=xy = -x: (x,y)ightarrow(y,x)(x, y) ightarrow (-y, -x)
  • Reflection across the origin: (x,y)ightarrow(x,y)(x, y) ightarrow (-x, -y)

Properties of Reflection

Reflections have distinct mathematical properties that govern how geometric shapes behave under the transformation:

  • Isometry (Distance-Preserving): The distance between any two points in the original shape is identical to the distance between their corresponding reflected points.
  • Angle-Preserving: The angles of a polygon remain unchanged. The original shape and the reflected shape are congruent.
  • Orientation Reversal: The orientation of the shape is reversed. For example, a clockwise triangle will become counter-clockwise when reflected.
  • Involutive (Double Reflection): Reflecting a shape twice across the same line returns it to its original position: R(R(P))=PR(R(P)) = P.