Since we know that x3 + y3 + z3 – 3xyz = (x + y + z)( x2 + y2 + z2 – xy – yz - zx)

Using (1) and (2) & x + y + z = 9

⇒ x3 + y3 + z3 – 3xyz = 81 × 9

∴ x3 + y3 + z3 – 3xyz = 729

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