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 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.

This site teaches Statistics and Probability to 7th graders through a series of 475 questions and interactive activities aligned to 10 Common Core mathematics skills.

This site teaches Expressions and Equations to 8th graders through a series of 4712 questions and interactive activities aligned to 32 Common Core mathematics skills.

This site teaches Functions to 8th graders through a series of 1920 questions and interactive activities aligned to 17 Common Core mathematics skills.

This site teaches Geometry to 8th graders through a series of 2398 questions and interactive activities aligned to 19 Common Core mathematics skills.

This site teaches Statistics and Probability to 8th graders through a series of 303 questions and interactive activities aligned to 5 Common Core mathematics skills.

This site teaches The Number System to 8th graders through a series of 676 questions and interactive activities aligned to 6 Common Core mathematics skills.

Although mom controls the oxygen source, the fetus has a couple of clever tricks to get the most oxygen possible! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Learn how the needs of the fetus are met by the placenta, which is a special organ that belongs to both the mother and the fetus! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Using the stethoscope to check blood pressure is a technique thatپگs been used for >100 years! Blood pressure is one of the major vital signs frequently measured by health care workers, and it tells us a lot about our blood circulation. Learn what blood pressure is, how it relates to resistance in a tube, why it is necessary to get oxygen to your cells, and how it can change as you age. Weپگll finally put it all together by relating pressure, flow, and resistance in one awesome equation!

No organ quite symbolizes love like the heart. One reason may be that your heart helps you live, by moving ~5 liters (1.3 gallons) of blood through almost 100,000 kilometers (62,000 miles) of blood vessels every single minute! It has to do this all day, everyday, without ever taking a vacation! Now that is true love. Learn about how the heart works, how blood flows through the heart, where the blood goes after it leaves the heart, and what your heart is doing when it makes the sound پàLub Dubجز.

Every time you take a breath, oxygen makes it way into your lungs. Follow along on that journey! Rishi is a pediatric infectious disease physician and works at Khan Academy.

In this 14-minute video lesson, Sal gives an overview of the cycles of regulation, de-regulation and government in 20th century US capitalism. [History playlist: Lesson 13 of 26]

In this 15-minute video lesson Sal gives an outline of the 1973 Allende Coup in Chile and Pinochet's Junta. [History playlist: Lesson 11 of 26]