In mathematics, an expansion of a product of sums expresses it as a sum of products by using the fact that multiplication distributes over addition - the opposite process of trying to write an expanded polynomial as a product is called polynomial factorization. "Expanding" means removing the ( ) ... but we have to do it the right way ( ) are called "parentheses" or "brackets" Whatever is inside the ( ) needs to be treated as a "package". So when multiplying: multiply by everything inside the "package". The table shows some examples of expansion. Railway tracks consist of two parallel metal rails joined together. Small gaps, called expansion gaps, are deliberately left between the rails as there is an expansion of the rails in hot weather. Water expands on heating.
In chapter 4, the students are taught about a process in which the contents of brackets are evaluated, the expansion. The chapter helps the students in recollecting the identities that were introduced in earlier classes. An identity is an equation that is true for all values of its variables.