I have to tell if the sum ∞∑n=1(−1)n1n+(−1)n+1
Converges or not. Can i use a comprasion test here? To assume that my sum is bigger than ∑∞n=1(−1)n1n+1? I dont think that's OK, but that's the only way I can think of right now.
Answer
How about this? Write out the series:
−1(11+1)+1(12−1)−1(13+1)+1(14−1)−1(15+1)....
=−12+1−14+13−16+15−18....
Then reorder terms...
1−12+13−14+15−16...
And it was the alternating harmonic series all along! Which has been proven to equal
∞∑n=1(−1)n+11n=ln(2)
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