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.
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