Rule method is another name of setbuilder form of sets.
There are two type of ways in which sets are expressed.
1. Set-builder form (rule method)
2.Roaster form
For example set A:{2,4,6,8......48} is in roaster form as it is writen in numericals but we can also expresse this set as set A : {all even numbers under 50} so it is in set builder form.