From Latin: adjacere - "lie near"
Definition: Two angles
that share a common side and a common
but do not overlap
Try this Drag the orange dot. The line AC is the common leg of the two adjacent angles
In the figure above, the two
share a common side (the blue line segment AC).
They also share a common
(the point A). They are therefore termed 'adjacent angles'.
Obviously, the larger angle ∠BAD is the sum of the two adjacent angles.
They do not overlap
In the figure on the right, the two angles
Although they share a common side (PS) and a common vertex (S), they are not considered adjacent angles
when they overlap like this.
Adjacent angles must be next to each other, not one on top of the other.
Another way of defining them is:
"two angles that share a side and a vertex, but do not share any
Another use of the term refers to the interior angles of polygons.
Any two interior angles that share a common side are called the "adjacent interior angles" of the polygon, or just "adjacent angles".
Here the word adjacent is used in its ordinary English meaning of "next to each other".
Other angle topics
(C) 2011 Copyright Math Open Reference. All rights reserved