Wolfram Research
Wolfram Math World: Sets
This page discusses sets and set theory in mathematics and probability, and it discusses the notation and properties of sets.
Wolfram Research
Wolfram Math World: Union
This page provides a good explanation of unions of sets in mathematics. It discusses the union of disjoint sets and the probabilities of unions, incorporating probabilities of the two independent sets and their intersection. Discusses...
Purple Math
Purplemath: Set Notation
This resource explains concepts related to set notation and gives examples for each.
California State University
California State University, San Bernardino: Inverse Functions
This site has many links to examples of inverse functions, including intersections, inverse by reflection, and graphing inverse functions.
Purple Math
Purplemath: Venn Diagrams
Introduces the basic terminology of Venn diagrams, and shows how to "populate" and read Venn diagrams.