After school, a F.5 student, Yan, discussed some mathematics matters with me, what a wonderful moment! One of the questions he asked was
“is it possible to define the cosine value of a vector?"
I just claimed that it is easy for finite dimensional or even countably infinite dimensional vector, for example, we may have something like
And actually, we may define where are vectors (even in different dimensional spaces). And it is just a beginning…
I don’t think I had asked my teachers something like that when I was a F.5 boy. Sharing and exploring mathematics is fun!