Regarding user Muphrid's answer to the posted question why do we use cosine as the expression of vector dot product?, would it be possible to pictorially express this thought/answer? It would be extremely useful, as I do not know how to determine the rotation in a given plane, therefore I cannot prove to myself that cosine is required in the dot product definition.
Thanks in advance. And, Thanks question OP Shams Tarek, Thanks Muphrid.