Does anyone know what type of factorization rule this exercise is?

[stiff prism]

i'm not completely sure what you asking

but if you are asking how one might go about solving it

one way is to look at the powers of a

a^12, a^6, a^18

you could find the hcf of the exponents

which in this case

is hcf of 6,12,18

that being 6

after that you could let a^6 = x

and see what the equation morphs into

you could then again plug a^6 = x

that might be one way to gain an insight in the factoring when your exponents are huge, but can get simplified this way

another way would be to notice that, a^18 + 3a^12 + 3a^6 + 1. a^18 and 1 are both cubes and there are 4 terms in the expression