We can use the below rules to judge two triangles are :
1.SSS(Side-Side-Side)(SSS): Triangles with equal sides on three sides are congruent triangles.
2.SAS(Side-Angle-Side)(SAS): A triangle whose sides and their angles correspond to each other is a congruent triangle.
3.ASA(Angle-Side-Angle)(ASA): The two corners and their sides correspond to equal triangles.
4.AAS(Angle-Angle-Side)(AAS): The opposite sides of the two corners and one of the corners correspond to equal triangles.
5.RHS(Right angle-Hypotenuse-Side)(HL): In a pair of right triangles, the hypotenuse is equal to the other right angle. (It proves to use the SSS principle)
But I don't know how to prove these rules to be true.