Question

which are cubes of a rational number?
8
-8
0.8
0.08
0.008

Answer 1

8 = 2^3 — yes.
-8 = (-2)^3 — yes.
0.8 = 4/5 = 2^2 / 5^1 — not a cube (prime exponents not multiples of 3).
0.08 = 2/25 = 2^1 / 5^2 — not a cube.
0.008 = 1/125 = (1/5)^3 — yes.

So the cubes of a rational number are 8, -8, and 0.008.