Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/math/algebra/x2f8bb11595b61c86:functions/x2f8bb11595b61c86:evaluating-functions/v/what-is-a-function Watch the next lesson: https://www.khanacademy.org/math/algebra2/functions_and_graphs/function-introduction/v/difference-between-equations-and-functions?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII Missed the previous lesson? https://www.khanacademy.org/math/algebra2/systems_eq_ineq/non-linear-systems-tutorial/v/systems-of-nonlinear-equations-3?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII Algebra II on Khan Academy: Your studies in algebra 1 have built...