## Prove that sum of three angles in a triange is 180°. Hence find the unknown value of ne from the given figure

Question

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## Answers ( )

Given :

A triangle ABC.

To prove :

∠A+∠B+∠C=180

o

⟹∠1+∠2+∠3=180

o

Construction :

Through A, draw a line l parallel to BC.

Proof :

Since l∥BC. Therefore,

∠2=∠4 …….eq(i)

And, ∠3=∠5……eq(ii)

adding eq(i)and(ii)

Therefore, ∠2+∠3=∠4+∠5

∠1+∠2+∠3=∠1+∠4+∠5 [adding∠1bothSide]

∠1+∠2+∠3=180

o

Thus, the sum of three angles of a triangle is 180

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solution