This art history video discussion examines Caspar David Friedrich's "Abbey among Oak Trees", 1809 or 1810, oil on canvas, 110.4 x 171 cm (Alte Nationalgalerie, Berlin).

This art history video discussion examines Caspar David Friedrich's "Monk by the Sea", 1808 or 1810, oil on canvas, 110 x 171.5 cm (Alte Nationalgalerie, Staatliche Museen zu Berlin).

This art history video discussion examines Caspar David Friedrich's "Solitary Tree (or Lone Tree)", 1822, oil on canvas, 55 x 71 cm (Alte Nationalgalerie, Berlin).

This art history video discussion examines Caspar David Friedrich's "Woman at a Window", 1822, oil on canvas, 44 x 73 cm (Alte Nationalgalerie, Berlin).

This site teaches Building Functions to High Schoolers through a series of 1355 questions and interactive activities aligned to 13 Common Core mathematics skills.

This site teaches Interpreting Functions to High Schoolers through a series of 3578 questions and interactive activities aligned to 38 Common Core mathematics skills.

This site teaches Linear, Quadratic, and Exponential Models to High Schoolers through a series of 137 questions and interactive activities aligned to 6 Common Core mathematics skills.

This site teaches Trigonometric Functions to High Schoolers through a series of 915 questions and interactive activities aligned to 15 Common Core mathematics skills.

This art history video discussion examines Henry Fuseli's "Titania and Bottom", c. 1790, oil on canvas, 2172 x 2756 mm (Tate Britain, London).

This art history video discussion examines The Paris Opera (1860-75) by architect Charles Garnier.

This art history video discussion examines Antoni Gaudi's Church of the Sagrada Familia or Basilica i Temple Expiatori de la Sagrada Familia Basilica, 1882- (consecrated 2, but still under construction), Barcelona, Spain.

This art history video discussion examines Paul Gauguin's "Nevermore", 1897, oil on canvas (Courtauld Gallery, London).

This art history video discussion examines Paul Gauguin's "The Red Cow", 1889, oil on canvas (LACMA).

Introduction to gel electrophoresis. How it's used to separate DNA fragments or other macromolecules.

This site teaches the Geometry of Circles to High Schoolers through a series of 1084 questions and interactive activities aligned to 9 Common Core mathematics skills.

This site teaches High Schoolers how to express geometric properties with equations through a series of 1721 questions and interactive activities aligned to 12 Common Core mathematics skills.

This site teaches High Schoolers Geometric Measurement and Dimension through a series of 82 questions and interactive activities aligned to 4 Common Core mathematics skills.

This geometry lesson shows that that an inscribed angle is half of a central angle that subtends the same arc. [Geometry playlist: Lesson 24 of 31]

This site teaches High Schoolers how to Interpret Categorical and Quantitative Data through a series of 45 questions and interactive activities aligned to 2 Common Core mathematics skills.