Two triangles are congruent if we can first triangle superimposes to second and get one the same triangle. The congruent triangles have the same size and shape. Congruent polygons. Three methods for showing triangles to be congruent. (sss) side -- side -- side. Equivalent sides of a triangle are equal. (sas) side -- angle -- side. Equivalent two sides of a triangle are equal and angle between them. (asa) angle -- side -- angle. Equivalent two angles and their common side of a triangle are equal.