Need help figuring out the sine, cosine, and tangent of an angle in a right triangle? Need to know how to solve a matrix-form linear equation in algebra? Need help solving problems involving 45°-45°-90° right triangles? You're in luck. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to systematically calculate sine, cosine and tangent in trigonometry.