Check past exams before teaching a hand computation

A student asked if a rare by-hand DFT case (N=8, k=5) was worth learning. Checking the seven past exams answered it: they only asked for k=0 and k=N/2 by hand, so the general angle case became one reference line with no practice. A useful pattern for last-minute prep is a recipe per skill with: how to spot it, the steps, the one thing to figure out, real variants, the trap, and what to skip. Only claim something is skippable when the assigned exam parts support it, and say that a new twist is still possible.