[tex]\it \mathcal{V}_{con} =\dfrac{\pi R^2h}{3},\ \ h= 2R\ \Rightarrow \mathcal{V}_{con} =\dfrac{\pi R^2\cdot2R}{3} \Rightarrow \mathcal{V}_{con} =\dfrac{2R^3\pi}{3} \ \ \ \ (1)\\ \\ \\ \ell_4=R\sqrt2,\ \mathcal{V} _{cub} =(R\sqrt2)^3 =2\sqrt2R^3\ \ \ (2)\\ \\ \\ (1), (2) \Rightarrow \dfrac{\mathcal{V}_{cub}}{\mathcal{V}_{con}}=\dfrac{2\sqrt2R^3}{\dfrac{2R^3\pi}{3}}=2\sqrt2R^3\cdot\dfrac{3}{2R^3\pi} =\dfrac{3\sqrt2}{\pi}[/tex]