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電子課本網(wǎng) › 第79頁

第79頁

信息發(fā)布者：
?$=(1+3+5+.….+15+17)+(\frac {1}{6}+ \frac {1}{12}+ \frac {1}{20}+ \frac {1}{72}+\frac {1}{90})$?
?$=81+(\frac {1}{2}-\frac {1}{3}+\frac {1}{3}-\frac {1}{4}+\frac {1}{4}-\frac {1}{5}+.….+\frac {1}{8}?\frac {1}{9}+\frac {1}{9}?\frac {1}{10})$?
?$=81+(\frac {1}{2}-\frac {1}{10})$?
?$=81+\frac {2}{5}$?
?$=81\frac {2}{5}$?
?$=1?\frac {1}{2}+1?\frac {1}{6}+1? \frac {1}{12} +.…. + 1-\frac {1}{90}$?
?$= 1 × 9?\frac {1}{2}+\frac {1}{6}+\frac {1}{12}+.….+\frac {1}{90})$?
?$=9?(1?\frac {1}{2}+\frac {1}{2}?\frac {1}{3}+\frac {1}{3}?\frac {1}{4}+...+\frac {1}{9}?\frac {1}{10})$?
?$=9?(1?\frac {1}{10})$?
?$=9?\frac {9}{10}$?
?$=8\frac {1}{10}$?
?$=(1+1+1+1+1+1+11)?(\frac {1}{2}+\frac {1}{4}+\frac {1}{8}$?
?$+\frac {1}{16}+\frac {1}{32}+\frac {1}{64}+\frac {1}{128})$?
?$=7?(1?\frac {1}{2}+\frac {1}{2}?\frac {1}{4}+\frac {1}{4}?\frac {1}{8}+\frac {1}{8}?\frac {1}{16}+\frac {1}{16}?\frac {1}{32}$?
?$+\frac {1}{32}?\frac {1}{64}+\frac {1}{64}?\frac {1}{128})$?
?$=7?(1?\frac {1}{128})$?
?$=7?\frac {127}{128}$?
?$=6\frac {1}{128}$?

$2$
$3$
$9$
$60$
$30$
$20$
答:去掉$\frac{1}{12}$和$\frac{1}{15}$這兩個分?jǐn)?shù)，才能使余下的分?jǐn)?shù)之和為1。
答：那么△與○的和是3。
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