In an isosceles triangle with base A, B, the angle at the apex C is 70 ° What is the outer angle of the triangle at the vertex A?

Since triangle ABC is isosceles, its angles at the base of AB are equal, angle CAB = CBA.
Then the angle CAB = СВA = (180 – ASB) / 2 = (180 – 70) / 2 = 55.
The angle DAС adjacent to the angle CAB, the sum of which is 180, then the angle DAС = (180 – CAB) = (180 – 55) = 125.
Answer: The outside angle at the vertex A is 125.