Tank A is a cube that holds 64,000 litres when full. Tank B is also a cube, with each edge twice as long as Tank A's, as shown. How many litres does Tank B hold? $(1{\text{m}}^3=1000$ litres)

Cube roots of negatives are real numbers (unlike square roots).

∛$(-n)$ = −∛$n$.

Example: ∛(−125). $125=5^3$. So ∛$(-125)=-5$.

This is one place where square root and cube root behave differently — square roots of negatives are NOT real (they're imaginary, a Class 11 topic). Cube roots of negatives are perfectly normal.