$\displaystyle \frac{\sqrt{3}}{6}\pi a^3$\displaystyle \frac{\sqrt{3}}{6}\pi a^3

$\displaystyle \frac{\sqrt{3}}{8}\pi a^3$\displaystyle \frac{\sqrt{3}}{8}\pi a^3

$\displaystyle \frac{\sqrt{3}}{12}\pi a^3$\displaystyle \frac{\sqrt{3}}{12}\pi a^3

$\displaystyle \frac{\sqrt{3}}{24}\pi a^3$\displaystyle \frac{\sqrt{3}}{24}\pi a^3