n → ∞ lim 1 9 + 2 9 + 3 9 + 4 9 + 5 9 + . . . + n 9 9 n ( 1 8 + 2 8 + 3 8 + 4 8 + 5 8 + . . . + n 8 ) = ?
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Not a solution, but it could be a hint towards one of the methods to solve this: https://en.wikipedia.org/wiki/Euler%E2%80%93Maclaurin_formula
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Relevant wiki: Sum of n, n², or n³
L = n → ∞ lim 1 9 + 2 9 + 3 9 + ⋯ + n 9 9 n ( 1 8 + 2 8 + 3 8 + ⋯ + n 8 ) = n → ∞ lim ∑ k = 1 n k 9 9 n ∑ k = 1 n k 8 = n → ∞ lim 2 0 1 ( 2 n 1 0 + 1 0 n 9 + 1 5 n 8 − 1 4 n 6 + 1 0 n 4 − 3 n 2 ) 9 n ⋅ 9 0 1 ( 1 0 n 9 + 4 5 n 8 + 6 0 n 7 − 4 2 n 5 + 2 0 n 3 − 3 n ) = n → ∞ lim 2 n 1 0 + 1 0 n 9 + 1 5 n 8 − 1 4 n 6 + 1 0 n 4 − 3 n 2 2 ( 1 0 n 1 0 + 4 5 n 9 + 6 0 n 8 − 4 2 n 6 + 2 0 n 4 − 3 n 2 ) = n → ∞ lim 2 + n 1 0 + n 2 1 5 − n 4 1 4 + n 6 1 0 − n 8 3 2 ( 1 0 + n 4 5 + n 2 6 0 − n 4 4 2 + n 6 2 0 − n 8 3 ) = 1 0 Using Faulhaber’s formula Divide up and down by n 1 0
Reference: Faulhaber's formula