∑ 1 ∞ ( 2 n + 9 ) ( n ) ( n + 8 ) n + 9
State your answer to 5 decimal places.
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In response to Kartik Sharma : There is a typo of sign (+) coming from third line.
n ( n + 8 ) n + 9 = 8 n 9 − 8 ( n + 8 ) 1
Eight lines of Python will work just fine.
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∑ n = 1 ∞ ( 2 n + 9 ) ( n ) ( n + 8 ) n + 9
= ∑ n = 1 ∞ ( 2 n + 9 ) 1 × n ( n + 8 ) n + 9
= ∑ n = 1 ∞ ( 2 n + 9 ) 1 ( 8 ( n ) 9 + 8 ( n + 8 ) 1 )
= ∑ n = 1 ∞ ( 2 n + 1 2 ) 1 ( n 9 ) + ∑ n = 1 ∞ ( 2 n + 1 2 ) 1 ( n + 8 1 )
= 2 1 2 9 ( ∑ n = 1 ∞ 2 n ( n ) 1 ) + 2 1 2 1 ( ∑ n = 1 ∞ 2 n ( n + 8 ) 1 )
Now, ∑ n = 1 ∞ 2 n ( n ) 1 = l n 2
let x = n + 8 in the 2nd series,
= 2 1 2 9 ( l n 2 ) + 2 1 2 1 ( ∑ x = 9 ∞ 2 x − 8 ( x ) 1 )
= 2 1 2 9 ( l n 2 ) + 2 1 2 2 8 ( ∑ x = 9 ∞ 2 x ( x ) 1 )
= 2 1 2 9 ( l n 2 ) + 2 1 2 2 8 ( l n 2 − ∑ n = 1 8 2 n ( n ) 1 )
Now, computing all that, we get the value as -
≈ 0 . 0 0 1 4 9