Constructing triangles with a compass – congruence criteria

MathematicsPlane GeometryAges 12–13

Construct triangle ABC step by step as if using a ruler and compass: the SSS case (three sides), the SAS case (two sides and the included angle), and the ASA case (one side and two adjacent angles). Click 'Next step' to draw the side, arcs, or rays; drag the free test point A and see that only two positions (mirror images across BC) satisfy the condition — the triangle is uniquely determined, which is the meaning of the congruence criteria.