Question 31177
if angle 4 and 2 are lying a line, then 4+2 is 180 degree. only thing u need see is that angle 4 and angle 2 are in a line.
if angle 3=1, then angle 2 is equal to the exterior of 3 (left side of 3).
then u see that angle 4 and the exterior of 3 (which is the same value of 2) are lying in a line which will give u 4+2 is 180 degree. (thank u for new drawing)