http://ItsMyAcademy.com/Set-Theory/ For List of Set Theory Tutorial videos. To write interval form of set into set builder form first we should know properly from which point our interval start and at which point it finishes. After that to write in set builder form we can use mathematical language of symbols. Defining X as the element of that set now write what is X and x represents which types of number. those all we have to mention there so that anyone reading the set builder form of set should be able to predict the elements of that set.