Been going through Gabriel Gambetta's Computer Graphics from Scratch aaand I'm confused about some #math

In the included picture... Is the second equation's double bars supposed to signify absolute value or magnitude/length of vector? Context makes it seem like the latter but I thought that was double bars?

The third equation: is there a reason the parens have sharp angles? Why is there a comma instead of a * (multiplication)?

Would appreciate any pointers in the right direction!

rust + godot + blender + gfx

Joined Nov 2017