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Kitty [74]
2 years ago
11

Prouvez par récurrence que quel que soit n EN\{0}, on a

Mathematics
1 answer:
Vanyuwa [196]2 years ago
6 0

The left side is equivalent to

\displaystyle \sum_{k=1}^n \frac1{k(k+1)}

When n = 1, we have on the left side

\displaystyle \sum_{k=1}^1 \frac1{k(k+1)} = \frac1{1\cdot2} = \frac12

and on the right side,

1 - \dfrac1{1+1} = 1 - \dfrac12 = \dfrac12

so this case holds.

Assume the equality holds for n = N, so that

\displaystyle \sum_{k=1}^N \frac1{k(k+1)} =1 - \frac1{N+1}

We want to use this to establish equality for n = N + 1, so that

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = 1 - \frac1{N+2}

We have

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = \sum_{k=1}^N \frac1{k(k+1)} + \frac1{(N+1)(N+2)}

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = 1 - \frac1{N+1} + \frac1{(N+1)(N+2)}

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = 1 - \frac{N+2}{(N+1)(N+2)} + \frac1{(N+1)(N+2)}

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = 1 - \frac{N+1}{(N+1)(N+2)}

\displaystyle \sum_{k=1}^{N+1} \frac1{k(k+1)} = 1 - \frac1{N+2}

and this proves the claim.

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Answer:

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Step-by-step explanation:

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