The sum of three numbers in ap is 12 and sum of their cubes is 288
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• Let three numbers be (a - d), a, (a + d).
» The sum of three numbers in ap is 12.
→ a - d + a + a + d = 12
→ 3a = 12
→ a = 4
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» Sum (let numbers) of their cubes is 288.
→ (a - d)³ + (a)³ + (a + d)³ = 288
(a + b)³ = a³ + b³ + 3a²b + 3ab²
(a - b)³ = a³ - b³ - 3a²b + 3ab²
→ a³ + d³ + 3a²d + 3ad² + a³ + a³ - d³ - 3a²d + 3ad² = 288
→ 3a³ + 6ad² = 288
→ 3(4)³ + 6(4)d² = 288
→ 192 + 24d² = 288
→ 24d² = 96
→ d² = 4
→ d = ±2
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Now..
› Take a = 4 and d = - 2
• (a - d) = 4 - (-2) = 4 + 2
=> 6
• a = 4
• (a + d) = 4 + (-2) = 4 - 2
=> 2
› Take a = 4 and d = +2
• (a + d) = 4 + 2
=> 6
• a = 4
• (a - d) = 4 - 2
=> 2
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A.P : 2, 4, 6 or 6, 4, 2
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