Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/precalculus/precalc-matrices/zero-identity-matrix-tutorial/e/zero-and-identity-matrices?utm_source=YT&utm_medium=Desc&utm_campaign=Precalculus Watch the next lesson: https://www.khanacademy.org/math/precalculus/precalc-matrices/zero-identity-matrix-tutorial/v/zero-matrix?utm_source=YT&utm_medium=Desc&utm_campaign=Precalculus Missed the previous lesson? https://www.khanacademy.org/math/precalculus/precalc-matrices/zero-identity-matrix-tutorial/v/identity-matrix?utm_source=YT&utm_medium=Desc&utm_campaign=Precalculus Precalculus on Khan Academy: You may think that precalculus is simply the course you take before calculus. You would be right, of course, but that definition doesn't mean anything unless you have some knowledge of what calculus is. Let's keep it simple, shall we? Calculus is a conceptual framework which provides systematic techniques for solving problems. These problems are appropriately applicable to analytic geometry and algebra. Therefore....precalculus gives you the background for the mathematical concepts, problems, issues and techniques that appear in calculus, including trigonometry, functions, complex numbers, vectors, matrices, and others. There you have it ladies and gentlemen....an introduction to precalculus! ... https://www.youtube.com/watch?v=l7p1X5pdDoc Note: All Khan Academy content is available for free at (www.khanacademy.org)

Watch Sal work through a basic Manipulating quadratic and exponential expressions problem. Watch the next lesson: https://www.khanacademy.org/test-prep/new-sat/new-sat-math/new-sat-passport-advanced-mathematics/v/sat-math-p2-harder?utm_source=YT&utm_medium=Desc&utm_campaign=NewSAT Missed the previous lesson? https://www.khanacademy.org/test-prep/new-sat/new-sat-math/new-sat-passport-advanced-mathematics/v/sat-math-p1-harder?utm_source=YT&utm_medium=Desc&utm_campaign=NewSAT New SAT (starting March 2016) on Khan Academy: Practice all of the skills you’ll need for the new SAT. We also have four official practice exams from College Board. The October 2015 PSAT is in the style of the new SAT. About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content. ... https://www.youtube.com/watch?v=nGjXhxjnlDQ Note: All Khan Academy content is available for free at (www.khanacademy.org)

When two objects interacting through a field change relative position, the energy stored in the field is changed. Khan Academy is a nonprofit organization with the mission of providing a free, world-class education for anyone, anywhere. We offer quizzes, questions, instructional videos, and articles on a range of academic subjects, including math, biology, chemistry, physics, history, economics, finance, grammar, preschool learning, and more. We provide teachers with tools and data so they can help their students develop the skills, habits, and mindsets for success in school and beyond. Khan Academy has been translated into dozens of languages, and 15 million people around the globe learn on Khan Academy every month. As a 501(c)(3) nonprofit organization, we would love your help! Donate or volunteer today! Donate here: https://www.khanacademy.org/donate Volunteer here: https://www.khanacademy.org/contribute ... https://www.youtube.com/watch?v=rMNJfR168_U Note: All Khan Academy content is available for free at (www.khanacademy.org)

Owing to their adaptability, their skill in communications, and their reputation for ferocity, the Mongols swept across Eurasia over the 13th and 14th centuries, quickly assembling the largest contiguous empire in world history. These non-state actors had to quickly learn how to become a state themselves. ... https://www.youtube.com/watch?v=n-7xGKl2HX4 Note: All Khan Academy content is available for free at (www.khanacademy.org)