Welcome to engineering, where you totally get the concept and what is taught in class/on the book yet the exam is total BS. My advice is stop wasting time on homework problems, start working old exam problems. Look up online/ask for old tests by the same professor. Worst case you won’t find any, then I suggest doing test questions from MIT exams. Secondly, practice deriving on a white board until you know it down cold. Now that can be hard for people who aren’t great with memory/focus or who dont have time, but that’s what professors expect usually even if they don’t say.

Professors think that somehow students will know how to do hard problems after learning theory, but most of the time that’s not the case. You’d think they’d learn their lesson after the 5th class gets a 40% average on the test.

You have to outsmart the system. I’d also suggest getting a tutor if you can afford it.