Question

Prove that the sum of the angles of the triangle is ${180}^{\circ }$.

Answer 1

$\angle 1+\angle 2+\angle 3={180}^o$

$xy$ and $QR$ are $||$

for lines $xy$ & $QR$

$\angle 2=\angle 4$

for lines $xy$ & $QR$

$\angle 3=\angle 5$

$\angle 1+\angle 4+\angle 5={180}^o$

$\angle 1+\angle 2+\angle 3={180}^o$

Hence, sum of all angles of $△$ are equal.