Question

Part I: Angle Sum Relationships

Answer 1

Answer with explanation:

→→The three Angles form a Linear pair.That is

 ⇒∠1+∠2+∠3=180°

→→When these three congruent triangles are joined they form a Trapezoid.

→→Sum of angles in a trangle is given by Angle sum property Axiom of triangle which states that sum of the angles in a triangle is 180°.

Answer 2

The three angles are adjacent to each other.
They appear to form a straight line.
It means that the sum of the three angles of a triangle is appears to be 180 degrees.