In ASA congruence, which parts are congruent?

• A. Two sides and the included angle
• B. Two angles and the non-included side
• C. Two angles and the included side
• D. All three sides

Answer: (C)

ASA congruence says that if two angles in one triangle are equal to two angles in another triangle and the side between those two angles is equal to the corresponding side, then the triangles are congruent. The crucial point is that the side used must lie between the two given angles—the included side. Knowing two angles fixes the shape of the triangle, and the included side fixes its size, leaving no room for a different triangle to match. The other described combinations correspond to different criteria: two sides with the included angle is SAS, all three sides is SSS, and two angles with a non-included side is AAS. The ASA condition specifically requires two angles and the included side.