An animated demonstration showing how to use a protractor to draw an angle
Math Open Reference

How to copy a triangle with compass and straightedge
Math Open Reference

Congruent triangles  all three sides equal. SSS
Math Open Reference

Congruent triangles  Why SSA does not work
Math Open Reference

Congruent triangles  Two sides and included angle. SAS
Math Open Reference

Polygons are congruent when all corresponding sides and interior angles are congruent.
Math Open Reference

Definition and properties of the inscribed angle of a circle
Math Open Reference

Definition and properties of vertical (or opposite) angles
Math Open Reference

Definition and properties of supplementary angles  two angles that add to 180 degrees
Math Open Reference

Definition and properties of the interior angles of a transversal
Math Open Reference
