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

July 26, 2021 | education

| **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.

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