Thread: Simple question about angle between two vectors

http://upload.wikimedia.org/math/7/7...8706d780f6.png
What do the two lines on each side of the vectors mean?

They mean the absolute value of u and v i.e, u and v are non-negative.

those aren't absolute values, those are norms.

See

http://en.wikipedia.org/wiki/Norm_(mathematics)

Indeed, apparently im a bit rusty on the old geometry.