Read this article and watch the videos. Pay attention to the terminology that it introduces about isosceles triangles. The base angle theorem states that the base angles of an isosceles triangle must be congruent. Do not focus on the proof. Pay attention to the examples of how to recognize congruent angles, measure vertex angles, and measure base angles.
Then, complete review questions 1–5 and check your answers.
Click https://www.ck12.org/geometry/isosceles-triangles/lesson/Isosceles-Triangles-GEOM/ link to open resource.