I don't understand the roster method and set notations and my teacher is very unhelpful

The roster method is defined as a way to show the elements of a set by listing the elements inside of brackets. An example of the roster method is to write the set of numbers from 1 to 10 as {1,2,3,4,5,6,7,8,9 and 10}. An example of the roster method is to write the seasons as {summer, fall, winter and spring}.SymbolMeaningExample{ }Set: a collection of elements{1, 2, 3, 4}A ∪ BUnion: in A or B (or both)C ∪ D = {1, 2, 3, 4, 5}A ∩ BIntersection: in both A and BC ∩ D = {3, 4}A ⊆ BSubset: every element of A is in B.{3, 4, 5} ⊆ D

if you're teacher are unhelpful you should complain it to your parents