Bài 8:
ta có: \(B=\left(\dfrac{1}{2}-1\right)\left(\dfrac{1}{3}-1\right)\left(\dfrac{1}{4}-1\right)\cdot...\cdot\left(\dfrac{1}{2007}-1\right)\left(\dfrac{1}{2008}-1\right)\)
\(=\dfrac{-1}{2}\cdot\dfrac{-2}{3}\cdot\dfrac{-3}{4}\cdot...\cdot\dfrac{-2006}{2007}\cdot\dfrac{-2007}{2008}\)
\(=-\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot...\cdot\dfrac{2006}{2007}\cdot\dfrac{2007}{2008}\)
\(=-\dfrac{1}{2008}\)
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