Expand $(1-2x)^{-3}$ up to and including the term in $x^3$, and state the open range of validity

Question

Expand $(1-2x)^{-3}$ up to and including the term in $x^3$, and state the open range of validity.[5]

Accepted Answer

$1+6x+24x^2+80x^3+\cdots;\ -\frac12<x<\frac12$

A negative integer power