If the side of a triangle are produced in order, Prove that the sum of the exterior angles so formed is equal to four right angles.

Proof

In triangle ABC,

=+ ________________ (i)

=+________________ (ii)

=+________________ (iii)

Adding equation (i), (ii) and (iii),

++= 2(++)

⇒ ++= 2(180°) [Sum of angles of triangle]

⇒ ++= 360°Proved.