The volume of a rhombic triacontahedron is calculated by utilising the formula: $$V = 4a^3 \sqrt{ 5+2 \sqrt{5}}$$ where $a$ is the length of an edge.
The rhombic triacontahedron is a polyhedron with a thirty faces; it is a Catalan solid and zonohedron.
Could someone kindly provide me with some insight as to why the formula contains $\sqrt{5}$, featured twice?