If ∝, β are the roots of x2 + px + 1 = 0, γ, δ the roots of x2 + qx + 1 = 0, then (∝ - γ)( β -γ)(∝+ δ)( β +δ) =
q2 - p2
α+β=-p , αβ=1 also γ2+1=-qγ and δ2+1= -qδ
(∝ - γ)( β -γ)(∝+ δ)( β +δ)= (αβ-(α+β)γ+γ2)(αβ+(α+β)δ+δ2)
=(γ2+pγ+1)(δ2-pδ+1)= (pγ-qγ)(-pδ-qδ)=(q2-p2)λδ=(q2-p2)