Apply the SSS and SAS Postulates to prove two triangles congruent, correctly identifying the included angle.
We now have real shortcuts for proving two triangles congruent: instead of matching all three sides AND all three angles, a few matching parts are enough to guarantee the rest come along for free. The Side-Side-Side (SSS) Postulate says that if all three sides of one triangle are congruent to the three corresponding sides of another, the two triangles are congruent -- no angles need to be checked, because only one triangle shape is possible from three fixed side lengths.
The Side-Angle-Side (SAS) Postulate needs two sides and the angle BETWEEN them -- the included angle, the one actually formed by those two specific sides. If two sides and the included angle of one triangle are congruent to the corresponding two sides and included angle of another, the triangles are congruent. The word "included" matters: the angle must be sandwiched between the two named sides, or the shortcut does not apply.
Mastery looks like: They correctly identify whether SSS or SAS applies to a pair of triangles, including correctly identifying the included angle, and use it to justify a congruence statement.
Common stumbles: Trying to apply SAS when the given angle is not actually between the two given sides; forgetting to state the Reflexive Property for a side shared by both triangles.