Or even better in some contexts is the form x² + b² = 2ax, in which case we have a = ½(x₁ + x₂) [the arithmetic mean of the roots] and b = √x₁x₂ [the geometric

Or even better in some contexts is the form x² + b² = 2ax, in which case we have a = ½(x₁ + x₂) [the arithmetic mean of the roots] and b = √x₁x₂ [the geometric mean of the roots], and the discriminant is a² – b², which has a nice symmetry.