Identification and Verification of the Properties of Triangle

Experiment 4: To verify that the exterior angle of a triangle is equal to the sum of its two opposite interior angles.
A B C D Figure I
A B C D Figure II
Figure Opposite interior angles Exterior angles Sum of two opposite interior angles Results
I. ∠ABC = ∠BAC = ∠ACD = ∠ABC + ∠BAC =
II. ∠ABC = ∠ACB = ∠CAD = ∠ABC + ∠ACB =
Conclusion: If any side of a triangle is produced, the exterior angle so formed is equal to the sum of the two opposite interior angles.