What does the word complement mean in maths?

Answer 1

In mathematics, the term "complement" refers to the concept of a set that includes all elements not in a given set, typically relative to a universal set. For example, if ( U ) is the universal set and ( A ) is a subset of ( U ), the complement of ( A ) (denoted as ( A' ) or ( U - A )) consists of all elements in ( U ) that are not in ( A ). In geometry, the complement can also refer to angles that add up to 90 degrees, such as the complement of a 30-degree angle being a 60-degree angle.