If every pair of the equations x2+px+qr=0 , x2+qx+rp=0 , x2+rx+pq=0 have a common root, then the sum of three common roots is
Let the roots be α, β; β, γ and γ, α respectively.
∴ α + β = -p, β + γ = -q, γ + α = -r
Adding all, we get ∑α = −(p+q+r)2 etc.