Congruence, Symmetry, and Transformations

Figures that are the same size and shape are congruent. Corresponding parts of congruent figures are congruent. Congruent figures, such as those at the right below, may be in different positions.

A figure has line symmetry if it can be folded in half so that the two halves match exactly. The line made by the fold is the line of symmetry. Line symmetry is also called bilateral symmetry. Figures can have any number of lines of symmetry, from no lines of symmetry to an infinite, or unlimited, number of lines of symmetry.

A figure has rotational symmetry if it can be rotated about a point less than a full turn to make the figure look the same as it did before the rotation.

Teaching Model 17.1: Congruent Figures