For this case, we have given an ABC triangle with internal angles α,β,γ. By definition, the sum of the internal angles must be 180 degrees.
That is to say:
α+β+γ=180
This can be demonstrated according to the fifth postulate of Euclid. From there we have to draw a parallel to one of the sides, by the vertex opposite him, the interior angles of the left side add two right angles.
Answer:
180 degrees
