Two angles are said to be complementary if their measures sum to a straight angle, i.e., to \(\pi\) radians or 180°. For example, a 40° angle is the complement of a 50° angle.

Graph Theory

The complement of a simple graph \(G\) is the simple graph having the same vertex-set and in which two vertices are adjacent if an only if they are not adjacent in \(G\).

Set Theory

If \(X\) is a set and \(A\) is a subset of \(X\), then the complement of \(A\) is the set of just those elements of \(X\) that are not in \(A\).