Question

if a side of triangle is pproduced then the exterirr angles so formed is equal to sum of the two interiror opposite angle

Answer 1

yes!!!!
it is right statement.....

Answer 2

Name the exterior angle has 4 and the interior angles 1,2,3
Now by angle sum property angle 1 + angle 2 + angle 3 is equal to 180 degree
An angle 3 + angle 4 is equal to 180 degree linear pair
Make them statements 1and2
From this week included angle 1 + angle 2 + angle 3 is equal to angle 3+ angle 4
cancel the angle 3 and you got the proof angle 1 + angle b is equal to angle 4