Prove that

Let Δ =

Applying Elementary Row Transformations

R₂→ R₂ – 2R₁

Δ =

R₃→ R₃ – 3R₁

Δ =

R₃→ R₃ – 3R₂

Δ =

Expanding Along C₁, we have

Δ = 1 (1 × 1 – 0 × (2 + p)) – 0 + 0

Δ = 1 – 0

Δ = 1

Hence, the given result is proved