- Lines a and b intersect forming two adjacent angles
- When lines a and b intersect, four angles formed, angle 1, angle 2, angle 3 and angle 4
- For angle 1, its adjacent angles are angle 2 and angle 3
- Therefore, when two lines intersect, the sum of its a pair of adjacent angles are 180 degrees.
- That is, every pair of adjacent angles are supplementary.