L.H.S =

Applying, R₁→R₁ + R₂ + R₃, we get,

Taking (a + b + c) common we get,

Applying C₂→C₂ – C₁ and C₃→C₃ – C₁, we get,

= (a + b + c)³ = R.H.S

Hence, proved.