# complement

### Geometry

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 $$A$$.