Oh I forgot to mention that of cause the matrices D and Y need to have the right dimension in order to do an matrix matrix multiplication but in your problem it is stated that both Y and D have the dimension n x 1 which is fine.
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I believe so. I'm not completely sure. I use trigonometry at work all the time for figuring out bends in pipe runs, but like I said, I haven't done mathematics like your question in ages.I love how someone downvoted me, meanwhile no one as of yet has even tried to supply you with any answer, let alone a correct answer. LOL
Lol, I have to get my diploma!
I am proud of you seriously.