Problem on basic theorm


Determine if each of the following objects is a member of Z;
{5}, {3, −1}, 7.12,√5, a = the 2,00th decimal digit in the base-10 expression for π


2000th decimal digit will be from 0 to 9 so it belongs to Z ,set of integers
{3,-1} is not a single integer so i think not belong to Z
7.12 also not a integer
is an irrational number (how do u proove it)