hey guys this is probably pretty basic stuff for most of you. im however struggling with this.

i don't have any standard procedure for this and i can't figure out how its done. i just don't know what kind of method i should be searching for.

in my course it was said you are already supposed to know how to do this so im lacking skill on this. here is the problem:

i underlined the equation where the polynomial is factorized. how to do this? whats the method called and how can i learn to do this on any generic 4th degree polynomial?