Câu hỏi của Đào An Nguyên

Question

Tính tổng: $\frac{1}{5.6}-\frac{1}{6.7}-\frac{1}{7.8}-...-\frac{1}{2004.2005}$

Phạm Diệu Hằng · Accepted Answer

$\frac{1}{5.6}$- $\frac{1}{6.7}$- $\frac{1}{7.8}$ - ... - $\frac{1}{2004.2005}$

= $\frac{1}{5}$- $\frac{1}{6}$+ $\frac{1}{6}$- $\frac{1}{7}$+ $\frac{1}{7}$- $\frac{1}{8}$+ ... + $\frac{1}{2004}$- $\frac{1}{2005}$

=$\frac{1}{5}$- $\frac{1}{2005}$

= $\frac{80}{401}$

Câu trả lời:

$\frac{1}{5.6}$- $\frac{1}{6.7}$- $\frac{1}{7.8}$ - ... - $\frac{1}{2004.2005}$

= $\frac{1}{5}$- $\frac{1}{6}$+ $\frac{1}{6}$- $\frac{1}{7}$+ $\frac{1}{7}$- $\frac{1}{8}$+ ... + $\frac{1}{2004}$- $\frac{1}{2005}$

=$\frac{1}{5}$- $\frac{1}{2005}$

= $\frac{80}{401}$