Question 132796
Linear pairs of angles are supplementary, meaning that the sum of their measures is 180.


That means that a1 + a2 = 180, which we can write as a1 = 180 - a2.


But we also know that a2 + a3 + a4 = 180, which we can write as a3 + a4 = 180 - a2.


Since a = b and c = b if and only if a = c, a3 + a4 = a1.