Talk:Cosine Formula for Dot Product

As of now there are some contradictions between this page and Definition:Angle Between Vectors recently put up.

A) the source I got "angle between vectors" from (Khan) prefers not to have to invoke vector arrows as part of the definition. I don't think I've created enough "vector arrow" pages to smooth over the differences/lack thereof between the two approaches.

B) Definition:Angle Between Vectors I put up defines the angle between $\mathbf{u,v}$ when $\mathbf{u} = c\mathbf{v}, c < 0$ as $\pi$. This page has it as zero.
 * Actually, that's probably a mistake, because $\cos 0 \ne -1$. --GFauxPas 14:37, 20 March 2012 (EDT)

C) Definition:Angle Between Vectors has the angle undefined if $\mathbf u$ or $\mathbf v$ are zero. This page has it defined, but I'm not entirely sure as what.

Suggestions? --GFauxPas 14:29, 20 March 2012 (EDT)