Question

If a side of a triangle is produce, then the exterior angle so formed is equal to the sum of the two interior opp. angles

Answer 1

in triangle ABC,
1+2+3=,180 (asp of triangle)i
4+3=180(linear pair) ii
from I&ii,
1+2+4=3+4
1+2=3
but, 3 is ext. opp angle.
hence proved!
hope it helps