How do you write in correct set notation?

Answer 1

e.g.

A = {2n-1 | n ∈ N} would give you all positive odd numbers.

B = { 1,2,3,4} would be the set B containing the integers 1,2,3,4

C = {x | -4 < x ≤ 5 , x ∈ R} would be the set of all real numbers between -4 and +5 excluding the -4 but including the +5

in general if you know the elements of the set, enclose them in { } brackets
the empty set or the null set is often written as Ø or {}

hope this helps,