Let us start with the original equation:

\((2a-1)^3\)

Splitting it up, or making it easier, we should put it into:

\((2a-1)(2a-1)(2a-1)\)

Multiplying the first two,:

\((4a^2-2a-2a+1)(2a-1)\)

Simplifying and Mathifying:

\((4a^2-4a+1)(2a-1) \\ =(8a^3-4a^2-8a^2+4a+2a-1) \\ =(8a^3-12a^2+6a-1)\)

So in the end, the answer is:

**(8a^3-12a^2+6a-1)**