Question

(3) Prove that the sum of angles of a triangle is 180°​

Answer 1

Step-by-step explanation:

In order to prove that the sum of angles of a triangle is 180, you must know the theorems of angles of a triangle.

We know that,  alternate interior angles are of equal magnitude.

This'll help us get the answer. Let us assume a triangle ABC. Now we have to substitute the angles.

∠PAB + ∠BAC + ∠CAQ = 180°. where PQ line parallel to side BC touching vertex A.

∠PAB = ∠ABC & ∠CAQ = ∠ACB BECAUSE alternate interior angles are congruent..

Hence we get, ∠ABC + ∠BAC + ∠ACB = 180°

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Answer 2

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



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