Suppose
On applying column operation C2 → C2 + C1
On taking (a + b + c) common
On applying row operation R2 → R2 - R1 and R3 → R3 - R1
On taking (b - c) and (c - a) common
= (a + b + c) (b – a) (c – a) (b – c)
Therefore, Δ = (a + b + c) (b – a) (c – a) (b – c)