I have troubles with any difference of squares expression that incorporates a fraction.

For instance in the expression $\displaystyle \frac{1}{64}x^6-1$

=$\displaystyle (\frac{1}{8}x^3-1)(\frac{1}{8}x^3+1)$

I understand the$\displaystyle x^3$ here comes from $\displaystyle x^{6/2}$, however I have no clue how we get $\displaystyle \frac{1}{8}$ from $\displaystyle \frac{1}{64}$. Would someone please enlighten me?

Thank you