Answer:
See proof below
Step-by-step explanation:
Find the diagram attached.
From the diagram, sum of angle on the straight line l is 180degrees that is:
<A' + <B' + <C' = 180° .... 1
Also note that
<A = <A' (corresponding angle) ...2
<B = <B' (corresponding angle) ... 3
<C = <C' (vertically opposite angle) ...4
Substitute 2, 3 and 4 into 1, we will have:
A+B+C = 180°
This shows that the sum of the interior angles of the triangle A B and C is 180°
