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I have a question about dot product for vector.

For detail : https://ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=st&chap_sec=02.4&page=theory

Is there anyone understand about it and explain to me the basic concept, why :

1. A • B = |A| |B| cosθ, not A • B =A^2 • B^2 - 2AB cosθ (Cosinus equation)

2. A|| = A cosθ u = (A • u) u (for vector component)

A|| = A • u (for direction component)

Thanks,

Ricky

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# Homework Help: Dot product for Vector equation

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