The document is a math lesson on isosceles triangles that includes definitions, theorems, examples and practice problems. It defines isosceles triangles as triangles with two congruent sides and base angles as the two angles adjacent to the base. It presents the Isosceles Triangle Theorem stating that if two sides are congruent, the angles opposite are also congruent. Examples show applying the theorem to find missing angle measures and side lengths. The Hypotenuse-Leg Congruence Theorem is introduced for right triangles. Practice problems have students identify if triangles can be proven congruent.