Answer:
∠1 = ∠4 and ∠3 = ∠5 ( alternate interior angle).
Step-by-step explanation:
Given : Triangle ABC with angle 1, 2, 3.
To find : Complete the statements to prove that the sum of the interior angles of ΔABC is 180°.
Solution : We have given that triangle ABC with angle 1, 2, 3.
Here, line DE and AC are parallel and BA is traversal line.
∠1 = ∠4 ( alternate interior angle)
∠3 = ∠5 ( alternate interior angle)
∠4 + ∠2+ ∠5 = 180 ( angle formed on line)
∠1 + ∠2 + ∠3 = 180.
Therefore, ∠1 = ∠4 and ∠3 = ∠5 ( alternate interior angle).