Question

proof that sum of all angel of triangle is 180°

Answer 1

Consider a triangle PQR and ∠1, ∠2 and ∠3 are the angles of ΔPQR (figure shown below). We need to prove that ∠1 + ∠2 + ∠3 = 180�.

XPY is a line.
∴∠4 + ∠1 + ∠5 = 180� … (1)
But XPY || QR and PQ, PR are transversals.
So, ∠4 = ∠2 and ∠5 = ∠3 (Pairs of alternate angles)
Substituting ∠4 and ∠5 in (1), we get
∠2 + ∠1 + ∠3 = 180�
∴∠1 + ∠2 + ∠3 = 180�

Touch the fig (TrianglePQR) to view it completely

Answer 2

Sum of all angles of triangle=180
x+x+x=180
3x=180
x=180÷3
x=60

So
60+60+60=180,Proved