This art history video examines the "Alexander Mosaic" c. 100 B.C.E., tessera mosaic from the House of the Faun, Pompeii. This Roman floor mosaic may be based on a lost Hellenistic painting by Philoxenos of Eretria, The Battle of Issus, c. 315 B.C.E.). Museo Archeologico Nazionale, Naples.

This site teaches Arithmetic with Polynomials and Rational Expressions to High Schoolers through a series of 4333 questions and interactive activities aligned to 26 Common Core mathematics skills.

This site teaches High Schoolers how to create equations through a series of 298 questions and interactive activities aligned to 5 Common Core mathematics skills.

This site teaches Reasoning with Equations and Inequalities to High Schoolers through a series of 5909 questions and interactive activities aligned to 36 Common Core mathematics skills.

This site teaches Structure in Algebraic Expressions to High Schoolers through a series of 3482 questions and interactive activities aligned to 26 Common Core mathematics skills.

How can we improve the speed of a (deterministic) primality test? Created by Brit Cruise.

Allele frequencies in populations and how they differ from genotype frequencies. Created by Sal Khan.

A gene as a stretch of DNA on a chromosome. Alleles as versions (sequence variants) of a gene.

Outline of the 1973 Allende Coup in Chile and Pinochet's Junta (this video under CC-BY-SA). Created by Sal Khan.

There are a number of European alliances that contributed to the broad scope of World War I. Prominent among these are the 1839 Treaty of London, which promised that the United Kingdom would protect Belgium's neutrality, the 1879 Dual Alliance treaty between Germany and Austria-Hungary to protect each other in the event of Russian attack, the 1892 Franco-Russian Military Convention that promised mutual assistance in the face of attack, the Triple Entente linking the United Kingdom and France (and later Italy), and the Triple Alliance linking Germany, Austria-Hungary, and Italy (at first). Created by Sal Khan.

This art history video discussion examines Washington Allston's "Elijah in the Desert", 1818, oil on canvas, 125.09 x 184.78 cm / 49 1/4 x 72 3/4 inches (Museum of Fine Arts, Boston).

This art history video discussion examines Sir Lawrence Alma-Tadema's "A Reading from Homer", 1885, oil on canvas, (Philadelphia Museum of Art).

In this art history video discussion Beth Harris and Steven Zucker examine Albrecht Altdorfer's "The Battle of Issus," 1529, oil on panel. Alte Pinokothek, Munich.

In this art history video discussion Dr. Beth Harris and Dr. Steven Zucker consider Ambrogio Lorenzetti's series of frescos "Allegory of Good Government", "Effects of Good Government in the City and the Country", and "Allegory and Effects of Bad Government in the City and the Country" Siena c. 1337-40. Sala della Pace (Hall of Peace) also known as the Sala dei Nove (the Hall of the Nine), Palazzo Pubblico, Siena.

How the Chinese buying of American debt leads to lower interest rates. Created by Sal Khan.