What is the easiest way to get: $2+ \sqrt{-121} = (2+ \sqrt{-1})^3$ I was reading the book Seventeen equations have changed the world.
At some point, while the book was talking about complex numbers, I see this equation:
$2+ \sqrt{-121} = (2+ \sqrt{-1})^3$
Even if it's easy to proof the truth of this equivalence (it is enough to develop the two members),
I can't find an easy/good/fast way to obtain straight the identity. 
Can you help me? Does there exist a mathematical property that I'm missing?

If it is to prove:
$$2+11i=2+i+10i=2+i+(2+i)(2+4i)=(2+i)(3+4i)=(2+i)(2+i+1+3i)=(2+i)(2+i+(2+i)(1+i))=(2+i)(2+i)(2+i).$$
