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Prove by induction: $$ \sum_{k=1}^{2n}(-1)^{k+1}\frac{1}{k} = \sum_{k=1}^{n}\frac{1}{n+k} $$

I start with (using $n = t+1$): $$ \sum_{k=1}^{2t+2}(-1)^{k+1}\frac{1}{k}=... $$

but after expanding and attempting to simplify I get stuck at: $$ \sum_{k=1}^{t}\frac{1}{t+k} + (-1)^{2t}\frac{1}{2t+2}-(-1)^{2t}\frac{1}{2t+1} $$

Any suggestions would be very helpful.

jdeeoh
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  • Show that the change in left hand side is same as the change in the right hand side as you go from $n$ to $n+1$. – Ujan Gangopadhyay Oct 16 '15 at 04:38
  • Consider there are 3200 questions about proving something by induction on this site. The title should be way more specific than "prove by induction" –  Oct 16 '15 at 04:41

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