An introduction to one of the most amazing ideas/numbers in mathematics Watch the next lesson: https://www.khanacademy.org/math/geometry/parallel-and-perpendicular-lines/Angle_basics/v/angle-basics?utm_source=YT&utm_medium=Desc&utm_campaign=Geometry Missed the previous lesson? https://www.khanacademy.org/math/geometry/intro_euclid/v/language-and-notation-of-the-circle?utm_source=YT&utm_medium=Desc&utm_campaign=Geometry Geometry on Khan Academy: We are surrounded by space. And that space contains lots of things. And these things have shapes.