There are four methods for ordinary triangles and five methods for right triangles.

(1) Angle: Two sides and their included angles are equal, and the two triangles are congruent. Abbreviated as (S.A.S)

(2) Angle and Angle: Two angles and their sides are equal, and the two triangles are congruent. Abbreviated as (A.S.A)

(3) Corner edge: two angles are equal to the edge opposite to one angle, and two triangles are congruent. Abbreviation: (A.A.S)

(4) Edge: Three edges are equal respectively, and these two triangles are congruent. Abbreviation: (S.S.S)

(5) The hypotenuse of the right-angle side: the hypotenuse is equal to one of the right-angle sides, and the two triangles are identical. Abbreviation: (H.L.)

The first four rules can be used for all triangles, and the fifth rule is only used for right-angled triangles.