What number sets does -8 belong to?

Answer 1

To any set that contains it!

It belongs to {-8},

or {-8, sqrt(2), pi, -3/7, 99.3},

or all whole numbers between -43 and 53,

or multiples of 2,

or integers,

or rational numbers,

or real numbers,

or complex numbers,

or square roots of 64

or fourth roots of 4096

etc.