Question

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

Answer 1

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
o
.
solution