Question

show that the sum of the angle of a triangle is two right angle​

Answer 1

Answer:

From External Angle of Triangle equals Sum of other Internal Angles: ... But from Two Angles on Straight Line make Two Right Angles, ∠ACB+∠ACD equals two right angles. So by Euclid's First Common Notion, ∠ABC+∠BAC+∠ACB equals two right angle