In triangle ABC, the angle at the vertex A is 55 degrees, AB = BC. Find the angle at the vertex B.

In triangle ABC, the angle at the vertex A is 55 degrees, AB = BC. Find the angle at the vertex B. Explain which theorem you used.

Since, according to the condition, AB = BC, then the triangle ABC is isosceles with the base AC, and then the angles at the base of the triangle are equal. Angle BAC = BCA = 55.

The sum of the interior angles of the triangle is 180, then the angle ABC = (180 – 55 – 55) = 70.

Answer: The angle at the vertex B is 70.



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.