The Higgs quartic coupling λ and vacuum expectation value v are free parameters in the Standard Model, chosen to reproduce the observed Higgs mass of 125.09 GeV. This paper proves they are not free. The Higgs potential V(φ) has its second derivative at the fixed point φ⁻¹ equal to exactly √5 — a direct consequence of the discriminant-5 axiom. From this, λ = 2φ/25 and m_H = 2v√φ/5 = 125.28 GeV. The Higgs mass is a theorem of discriminant-5 geometry. Route C of three possible derivation paths is established as the correct one.