Video first reviews that a function is invertible if and only if there is a unique solution to f(x) = y for any y. Extends this to show that a function is invertible if and only if it is surjective (onto) and injective (one-to-one). [6:31]

Video explains what a surjective or onto function is and also what an injective or one-to-one function is. Gives examples and non-examples of surjective and injective functions. [9:31]