Understanding what it means for a set to be closed under an operation. ... https://www.youtube.com/watch?v=BXg3cAbmDjM Note: All Khan Academy content is available for free at (www.khanacademy.org)

Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/algebra2/polynomial_and_rational/quad_factoring/e/solving_quadratics_by_factoring?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII Watch the next lesson: https://www.khanacademy.org/math/algebra2/polynomial_and_rational/quad_factoring/v/example-2-solving-a-quadratic-equation-by-factoring?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII Missed the previous lesson? https://www.khanacademy.org/math/algebra2/polynomial_and_rational/quad_factoring/v/factoring-polynomials-1?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII Algebra II on Khan Academy: Your studies in algebra 1 have built a solid foundation from which you can explore linear equations, inequalities, and functions. In algebra 2 we build upon that foundation and not only extend our knowledge of algebra 1, but slowly become capable of tackling the BIG questions of the universe. We'll again touch on systems of equations, inequalities, and functions...but we'll also address exponential and logarithmic functions, logarithms, imaginary and complex numbers, conic sections, and matrices. Don't let these big words intimidate you. We're on this journey with you! ... https://www.youtube.com/watch?v=2ZzuZvz33X0 Note: All Khan Academy content is available for free at (www.khanacademy.org)

Line of reflection example ... https://www.youtube.com/watch?v=435Ipnmp7bA Note: All Khan Academy content is available for free at (www.khanacademy.org)

Showing that the limit of sin(x)/x as x approaches 0 is equal to 1. If you find this fact confusing, you've reached the right place! Watch the next lesson: https://www.khanacademy.org/math/ap-calculus-ab/ab-derivative-rules/ab-derivtive-rules-opt-vids/v/1-cosx-over-x-as-x-approaches-0?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB Missed the previous lesson? https://www.khanacademy.org/math/ap-calculus-ab/ab-derivative-rules/ab-derivtive-rules-opt-vids/v/proof-d-dx-sqrt-x?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB AP Calculus AB on Khan Academy: Bill Scott uses Khan Academy to teach AP Calculus at Phillips Academy in Andover, Massachusetts, and heÕs part of the teaching team that helped develop Khan AcademyÕs AP lessons. Phillips Academy was one of the first schools to teach AP nearly 60 years ago. About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything. ... https://www.youtube.com/watch?v=5xitzTutKqM Note: All Khan Academy content is available for free at (www.khanacademy.org)