Given, (a – b – c) (a2 + b² + c² + ab + ac – bc)

= a³ + ab² + ac² + a²b + a²c – abc – a²b – b³ – bc² – ab² – abc + b²c – a²c – b²c – c³ – abc – ac² – bc²

Cancelling the terms with opposite signs,

= a³ – b³ – c³ – 3 abc