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第102頁

信息發(fā)布者：
?$\frac {1}{⑧}-\frac {1}{⑨}$?
?$=\frac {1}{7×8×9}- \frac {1}{8×9×10}$?
?$=\frac {1}{7}×\frac {1}{8}×\frac {1}{9}-\frac {1}{8}×\frac {1}{9}×\frac {1}{10}$?
?$=\frac {1}{9}×(\frac {1}{7}×\frac {1}{8}-\frac {1}{8}×\frac {1}{10})$?
?$=\frac {1}{9}×[\frac {1}{8}×(\frac {1}{7}-\frac {1}{10}))]$?
?$A=\frac {1}{8}×(\frac {1}{7}-\frac {1}{10})$?
?$=\frac {1}{8}×\frac {3}{70}$?
?$=\frac {3}{560}$?
1
$\frac{1}{64}$
$\frac{63}{64}$

$\begin{aligned}&\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\\=&\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}+\frac{1}{128}-\frac{1}{128}\\=&\frac{1}{4}-\frac{1}{128}\\=&\frac{31}{128}\end{aligned}$

$\begin{aligned}&\frac{7}{5}+\frac{7}{10}+\frac{7}{20}+\frac{7}{40}\\=&\frac{7}{5}+\frac{7}{10}+\frac{7}{20}+\frac{7}{40}+\frac{7}{40}-\frac{7}{40}\\=&\frac{7}{5}\times2-\frac{7}{40}\\=&\frac{21}{8}\end{aligned}$
?$\frac {1}{1×2×3}+\frac {1}{2×3×4}+·s+\frac {1}{98×99×100}=$?
?$(\frac {1}{1×2}-\frac {1}{2×3})×\frac {1}{2}+(\frac {1}{2×3}-\frac {1}{3×4})×\frac {1}{2}+·s+$?
?$(\frac {1}{98×99}-\frac {1}{99×100})×\frac {1}{2}=(\frac {1}{1×2}-\frac {1}{2×3}+$?
?$\frac {1}{2×3}-\frac {1}{3×4}+·s+\frac {1}{98×99}-\frac {1}{99×100})×\frac {1}{2}=$?
?$(\frac {1}{2}-\frac {1}{99×100})×\frac {1}{2}=\frac {4949}{19800}$?
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