[dalke]

"Use (x-y)(x+y)" is part of the "folk wisdom." It's between "We even know some folk wisdom intended to avoid the dangers." and "or is it increasing magnitude?", where the last bit shows that perhaps these aren't the best solutions.

[conistonwater]

No, later in the article they recommend using it, saying that it decreases floating-point errors.

[dalke]

Ahh! Yes, in the box on p94 titled "About That Folk Wisdom". Thanks for the correction!