the sum of three numbers in AP is 12 and sum of their cubes is 288 find the numbers
Answers
Answer:
The numbers are 2, 4 and 6.
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Step-by-step explanation:
Let a be the middle number and let d be the common difference. (It's handy to let a be the middle number rather than the fast number because it can make some of the algebra easier by keeping the numbers small.)
The three numbers are: a - d, a, a + d
Their sum is 12 => ( a - d ) + a + ( a + d) = 12 => 3a = 12 => a = 4
So the numbers are: 4 - d, 4, 4 + d
The sum of their cubes is 288
=> ( 4 - d )³ + 4³ + ( 4 + d )³ = 288
=> ( 4³ - 3×4²×d + 3×4×d² - d³ ) + 4³ + ( 4³ + 3×4²×d + 3×4×d² + d³ ) = 288
=> 3×4³ + 2×3×4×d² = 288
=> 24 d² = 288 - 3×4³ = 288 - 192 = 96
=> d² = 96 / 24 = 4
=> d = ±2
If d = -2, the numbers in order are 4 - (-2), 4, 4 + (-2)
If d = 2, the numbers in order are 4 - 2, 4, 4 + 2
Either way, the numbers are 2, 4 and 6.