Question

How does knowing the prefixes in- and ex- help you remember the difference between an intrusion and an extrusion?

Answer 1

in- means into or inside of
ex- means out
intrusion, is the act of pushing in as in intruder
extrusion, is the process of thrusting outwards

Answer 2

The prefix in- means in, on, or not. In this case, it means in.
The prefix ex- out of, from, or not. In this case, it means out of.

(In)trusion means the act of intruding, breaking, or invading. You are going IN a a situation or a place
(Ex)trusion means the act of extruding, force or pushing OUT. :)