2 5 6 + 1 2 8 ( 1 ≤ i ≤ 8 ∑ a i ) + 6 4 ( 1 ≤ i < j ≤ 8 ∑ a i a j ) + + 3 2 ⎝ ⎛ 1 ≤ i < j < k ≤ 8 ∑ a i a j a k ⎠ ⎞ + … + a 1 a 2 ⋯ a 7 a 8 = 1 1 1 5 4 6 4 3 5
There exist some positive integers a i for i = 1 , 2 , . . 8 such that they satisfy the above equation find the sum of all possible value of a 3
hint - 111546435 has quite interesting factors.
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Exactly! Nice work. Did you change the topic to number theory?
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Yeah I did it.
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Is the same way applicable if no. is double the no. in the question? Think about it
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@Kaustubh Miglani – Can you please elaborate?
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@Department 8 – Well same question just a little change,Here- 256+128(a1+a2....
................=111546435*2 There exist some positive integers a i for i = 1 , 2 , . . 8 such that they satisfy the above equation find the sum of all possible value of a 3
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@Kaustubh Miglani – It is pretty much tedious!
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@Department 8 – YES it is.As expected u answered correctly congrats
Too easy and a highly overrated problem
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Let x = 2 so the given equation becomes
x 8 + ⎝ ⎛ i = 1 ∑ 8 a i ⎠ ⎞ x 7 + ⎝ ⎛ 1 ≤ i < j ≤ 8 ∑ a i a j ⎠ ⎞ x 6 + ⎝ ⎛ 1 ≤ i < j < k ≤ 8 ∑ a i a j a k ⎠ ⎞ x 5 + . . . + i = 1 ∏ 8 a i = 1 1 1 5 4 6 4 3 5
Clearly this is equivalent to
i = 1 ∏ 8 ( x + a i ) = 1 1 1 5 4 6 4 3 5
Since 1 1 1 5 4 6 4 3 5 = 3 × 5 × 7 × 1 1 × 1 3 × 1 7 × 1 9 × 2 3 .
We assume that a 8 > a 7 > . . . . > a 1 then x + a 1 = 3 ⟶ a 1 = 1 . This means we can keep changing the inequality above like a 8 > a 7 > . . . > a 1 > a 2 this for 5 , 7 , 1 1 , 1 3 , 1 7 , 2 3 and will get 3 , 5 , 9 , 1 1 , 1 5 , 2 1 respectively so the sum of all values are
1 + 3 + 5 + 9 + 1 1 + 1 5 + 2 1 = 8 2 .
Things to note:
The sign ∑ i = 1 8 a i denotes a 1 + a 2 + . . . + a 8
The sign ∑ 1 ≤ i < j ≤ 8 a i a j denotes the product of all a i for i = 1 , 2 , . . . 8 taken two at a time, like in the expansion of ( x + 1 ) ( x + 2 ) ( x + 3 ) the coefficient of x denotes the product of 1, 2, 3 taken to at a time like 1 × 2 + 2 × 3 + 3 × 1 and similarly the rest signs of he summation denotes the same thing.
The sign ∏ i = 1 8 a i the denotes the product of all a i .