Theorem 6.7 - Chapter 6 Class 9 Lines and Angles

Last updated at August 5, 2026 by

Theorem 6.7 - Prove that sum of angles of triangles is 180 - Class 9 - Theorems

part 2 - Theorem 6.7 - Theorems - Serial order wise - Chapter 6 Class 9 Lines and Angles

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Theorem 6.7 :- The sum of all angles are triangle is 180°. Given :- Δ PQR with angles ∠1, ∠2 and ∠3 Prove :- ∠1 + ∠2 + ∠3 = 180° Construction:- Draw a line XY passing through P parallel to QR Proof: Also, for line XY ∠1 + ∠4 + ∠5 = 180° ∠1 + ∠2 + ∠3 = 180° Hence, sum of all angle of a triangles are equal. Hence proved

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