Question 1177468


mangle 1 + m angle2 + m angle 3 = 180 deg.  Sum of angles of triangle = 180 deg.


mangle 3 + mangle 4 = 180 deg. angles in a linear pair

Therefore 

mangle 1 + m angle2 + m angle 3 = mangle 3 + mangle 4

m angle 3 is common

mangle 1 + m angle2  = mangle 4