If yz−x2zx−y2xy−z2xz−y2xy−z2yz−x2xy−z2yz−x2zx−y2=r2u2u2u2r2u2u2u2r2, then

In the left-hand determinant, each element is the cofactor of the elements of the determinantx    y    zy    z    xz    x    y=Δ∗( say )Hence,Δ∗2=xyzyzxzxyxyzyzxzxy∣=x2+y2+z2xy+yz+zxxz+yx+zy ΣxyΣx2Σxy  ΣxyΣxyΣx2=r2u2u2u2r2u2u2u2r2 ∵x2+y2+z2=r2,xy+yz+zx=u2