5.1 Ray Sphere Intersection rationality

[kristopolous]

The statement "Recall that the equation for a sphere centered at the origin of radius R is x2+y2+z2=R2." is fairly lacking because "why squared" is never answered (nor for that matter what squaring a number is in this context but we can skip that).

It took me a few seconds to realize this is Pythogorean. A helpful math link such as to here http://mathcentral.uregina.ca/qq/database/qq.09.03/jaidev1.html or something equally brief would be of great assistance to people like me who are a bit impertinent that things get demonstrated