Angles Adjacent to a Side

In a polygon, an angle is referred to as an adjacent angle to a side if the vertex of the angle is an endpoint of that side.

In other words, an angle is adjacent to a side when that side is one of the sides that forms the angle.

For instance, angle alpha (α) is adjacent to side AB and side AC because vertex A, associated with angle alpha, is an endpoint of both sides AB and AC.

Similarly, angle beta (β) is adjacent to side AB and side BC, as vertex B is an endpoint of both sides AB and BC.

Finally, angle gamma (γ) is adjacent to side AC and side BC because vertex C is an endpoint of both sides AC and BC.

And so on.