Onto function: Learn the basics of one-to-one and onto

Learn the basics of one-to-one and onto functions in mathematics with easy definitions, key differences, and solved examples to help you understand function mapping better. Learn what an onto function is, how to check if a function is onto , and how to find the number of onto functions. See examples, graphs, and FAQs on onto functions. An onto function , also known as a surjective function , is a type of function where every element in the co-domain is mapped to at least one element in the domain. In other words, an onto function covers the entire codomain, ensuring that every possible output value is achieved by some input value. Learn what an onto (surjective) function is in Maths—clear definition, key differences, visual graphs, and stepwise methods to identify onto functions with solved examples and exam tips.