In an isosceles triangle, the outer angle is 40 degrees at the apex, find the angles of the triangle.

We have a triangle ABC, where ∠B is the apex of the triangle.
How to find the angle of the vertex, knowing its external?
It’s very simple, these corners are adjacent.
∠B = 180 ° – 40 ° = 140 °
Based on the fact that triangle ABC is isosceles – remember the rule. The angles at the base of an isosceles triangle are equal.
Hence, ∠A = ∠C
The sum of all the angles of a triangle is 180. If two are equal, and we know the third, then they are very easy to find through the equation.
∠B + ∠A + ∠C = 180 °
140 ° + 2∠A = 180 °
∠A = 20 °
Answer: ∠A = 20 °; ∠B = 140 °; ∠C = 20 °.