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

According to the condition of the problem, triangle ABC is isosceles, its sides are AB and AC, and the angle B is 70 °.

Side BC is the base of this isosceles triangle, and angle B is one of the angles at the base.

Since this triangle is isosceles, the angle C, which also lies at the base, is equal to the angle B and is 70 °.

Since the sum of the angles of any triangle is 180 °, we can write the following equation:

∠A + 70 + 70 = 180.

Solving this equation, we get:

∠A + 140 = 180;

∠A = 180 – 140;

∠А = 40 °.

Answer: Angle A is 40 °.