Angles in Opposite Segments are Supplementary
(add up to 180o).
| Note: | As long as X and Y are on opposite sides of AB, the sum Angle(AXB)+Angle(AYB) will always be equal to 180°, i.e. the two angles (in opposite segments) are supplementary. If X and Y are on the same side of AB, please refer to Property 3. |