In a triangle ABC A = 55 degrees AB = BC Find angle B.

1. It is known that:

a) the sum of the angles of the triangle is 180 *;

b) a sign of an isosceles triangle: if two sides of a triangle are equal, then such a triangle is isosceles;

c) property of an isosceles triangle: the angles at the base are equal.

2. By the condition of the problem, the sides of the triangle ABC are equal, which means that this triangle ABC is isosceles.

According to the property of an isosceles triangle, the angle A at the base is equal to the second angle at the base, angle C.

It is known that the angle A is equal to 55 *, hence the angle C is equal to 55 *.

3. Find angle B.

Angle B = 180 * – 55 * – 55 * = 70 *.

Answer: Angle B of triangle ABC is 70 *.