im looking for some help or how to set out this question:

find the supremum and infinum of the following sets of real numbers, justify answer. state whether they or not they are contained in the set

X = { $\displaystyle 1, \frac {1} {2^2}, \frac {1}{3^2}, \frac {1} {4^2}$, ..., $\displaystyle \frac {1}{n^2}$, ...}