$\displaystyle \sum_{r=1}^{20} \frac{1}{(r+3)(r+6)}$ Help, please? I'll never understand Series.
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$\displaystyle \frac{1}{(k+3)(k+6)} = \frac{1}{3}\left( \frac{ 1 }{k+3} - \frac{1}{k+6}\right)$.
Originally Posted by Silver $\displaystyle \sum_{r=1}^{20} \frac{1}{(r+3)(r+6)}$ Help, please? I'll never understand Series. If you're still stuck after reading TPH's reply, read Telescoping series - Wikipedia, the free encyclopedia
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