Question

prove that if side of a triangle is produced the exterior angle so formed is equal to the sum of interior angle

Answer 1

let in triangle ABC, BC is produced to E
therefore the exterior angle formed is ∠ ACE
we know that,
 A+B+C=180
          ∠C=180-(A+B)
and ∠ ACB+∠ACE=180  (Because linear pair)
therefore,
           ∠C+∠ ACE=180
180-(A+B)+∠ACE=180
                   ∠ACE=A+B
exterior angle is equal to sum of opp interior angles