# Triangle ABC – isosceles, AB = AC Angle B is 70 °. Find angle A.

May 29, 2021 | education

| It is known from the condition that the triangle ABC is isosceles, and the sides AB = AC are equal to each other. The degree measure of the angle B = 70 ° is also known.

In order to find the degree measure of the angle A, recall the theorem on the sum of the angles of a triangle.

The angles of a triangle add up to 180 °.

In an isosceles triangle, the angles at the base are equal. Angle A is the angle at the apex of the triangle, and angle B and C are the angles at the base and they are equal to each other.

Find the degree measure of the angle A:

180 ° – (70 ° + 70 °) = 180 ° – 140 ° = 40 °.

Answer: angle A = 40 °.

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