If p + m = 6 and p3 + m3 = 72, then the value of pm is

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If p + m = 6 and p³ + m³ = 72, then the value of pm is

1. 6
2. 12
3. 9
4. 8

Correct Option: D

Using Rule 8,
p + m = 6
On cubing both sides,
(p + m)³ = p³ + m³ + 3pm(p + m)
⇒ (6)³ = 72 + 3pm × 6
⇒ 216 – 72 = 18pm
⇒ 18pm = 144
⇒ pm = 144 ÷ 18 = 8