Cass 7 Maths online solutions-Triangle and its properties
Chapter 6 – Triangle and its properties Introduction
Exterior angle of a triangle and its properties
An exterior angle of a triangle can be formed by extending the sides of a triangle at its vertex. A triangle can have three exterior angles.
An exterior angle of a triangle is equal to the sum of its interior opposite angles.
Proof:-
Given – Consider ∆ABC
∠ACD is an exterior angle
To Show:-
M ∠ACD=m ∠A +m ∠B
Through C draw CE parallel to BA
∠1= ∠X (BA is parallel to CE and AC is a transversal so the alternate angle should be equal)
∠2= ∠y (BA is parallel to CE and AD is a transversal so the corresponding angle should be equal)
∠1+ ∠2= ∠x+ ∠y
As we know ∠x+ ∠y=m ∠ACD
So, ∠1+ ∠2= ∠ACD
Hence proved
The above relation proved between an exterior angle and its two interior opposite angles are referred as the exterior angle property of a triangle.
For examples and practice questions click on CBSE Class 7th Maths.
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