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The Maclaurin series for − ln ( 1 − x ) is n = 1 ∑ ∞ n x n for ∣ x ∣ < 1 .
In this case we have x = 1 − e 1 , and thus the given series has the value
− ln ( 1 − ( 1 − e 1 ) ) = − ln ( e 1 ) = − ln ( e − 1 ) = 1 .
Proof of series expansion: Note first that the derivative of − ln ( 1 − x ) is 1 − x 1 .
So for ∣ x ∣ < 1 we have that − ln ( 1 − x ) = ∫ 1 − x 1 d x =
∫ ( n = 0 ∑ ∞ x n ) d x = n = 0 ∑ ∞ ( ∫ x n d x ) = n = 0 ∑ ∞ n + 1 x n + 1 + C = n = 1 ∑ ∞ n + 1 x n + C .
Now since ln ( 1 ) = 0 we see that C = 0 , resulting in the aforementioned series representation.
Comments: For a discussion on the permissibility of exchanging summation and integral signs, see this link .
In general, for y ≥ 1 we have that n = 1 ∑ ∞ n ( 1 − y 1 ) n = ln ( y ) .