It's math I put surprisingly easy.

I recommend that you obtain an independent review of the homework on this course, specifically to address the questions of whether the course prepares learners for the homework, and whether the questions are are clear to learners. I find that the answers to these questions are NO for weeks 4 and 5. In week 5, for example, question 1(1) asks about a single state |phi-f> which is not defined in the question or in the introduction to the homework or in the lectures. Questions 1(2-5) use a technique that has not been taught in the lectures and is not always part of an undergraduate course in QM. This kind of thing can be extremely disappointing for learners, and frankly implies that the setter of the questions was not actually competent to do so.

Poor. Very boring and dull presentation. Hardly anything is explained very clearly. It would be far more profitable to simply study an appropriate textbook or online course notes.