\(\frac{1}{5.6}-\frac{1}{6.7}-\frac{1}{7.8}-...-\frac{1}{2016.2017}\)
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NS
6
HN
11 tháng 3 2018
\(\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+.........+\frac{1}{24.25}\)
= \(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-........-\frac{1}{24}+\frac{1}{24}-\frac{1}{25}\)
= \(\frac{1}{5}-\frac{1}{25}\)
= \(\frac{5}{25}-\frac{1}{25}\)
= \(\frac{4}{25}\)
11 tháng 3 2018
Ta có :
\(\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}\)
\(=\)\(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{24}-\frac{1}{25}\)
\(=\)\(\frac{1}{5}-\frac{1}{25}\)
\(=\)\(\frac{5}{25}-\frac{1}{25}\)
\(=\)\(\frac{4}{25}\)
Vậy \(\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}=\frac{4}{25}\)
Chúc bạn học tốt ~
PM
1
26 tháng 5 2020
\(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{3}-\frac{1}{8}=\frac{5}{24}\)
Ez :))
NT
3
T
10 tháng 4 2016
= 1/2 - 1/3 + 1/3 -1/4 +....+1/7 - 1/8
= 1/2 - 1/8
= 3/8
Ai mk mk lại !!
10 tháng 4 2016
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{2}-\frac{1}{8}\)
\(=\frac{3}{8}\)
15 tháng 7 2018
\(\frac{1}{9.10}-\frac{1}{8.9}-\frac{1}{7.8}-\frac{1}{6.7}-\frac{1}{5.6}-\frac{1}{4.5}-\frac{1}{3.4}-\frac{1}{2.3}-\frac{1}{1.2}\)
\(=-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\right)+\frac{1}{9.10}\)
\(=-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)+\frac{1}{90}\)
\(=-\left(1-\frac{1}{10}\right)+\frac{1}{90}\)
\(=-\frac{9}{10}+\frac{1}{90}\)
= ...
bn tự tính nha!
PY
0
NT
0
14 tháng 8 2016
\(B=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{9}-\frac{1}{10}\)
\(B=\frac{1}{3}-\frac{1}{10}\)
\(B=\frac{7}{30}\)
DA
1
3 tháng 7 2015
\(\frac{1}{5.6}\)- \(\frac{1}{6.7}\)- \(\frac{1}{7.8}\) - ... - \(\frac{1}{2004.2005}\)
= \(\frac{1}{5}\)- \(\frac{1}{6}\)+ \(\frac{1}{6}\)- \(\frac{1}{7}\)+ \(\frac{1}{7}\)- \(\frac{1}{8}\)+ ... + \(\frac{1}{2004}\)- \(\frac{1}{2005}\)
=\(\frac{1}{5}\)- \(\frac{1}{2005}\)
= \(\frac{80}{401}\)
L
7 tháng 5 2018
\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{24}-\frac{1}{25}\)\(\frac{1}{25}\)
\(A=\frac{1}{5}-\frac{1}{25}\)
\(A=\frac{5}{25}-\frac{1}{25}=\frac{4}{25}\)
7 tháng 5 2018
\(A=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{24.25}\)
\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{24}-\frac{1}{25}\)
\(A=\frac{1}{5}-\frac{1}{25}\)
\(A=\frac{4}{25}\)
1/5.6 - 1/6/7 - 1/7.8 - ...- 1/2016.2017
= 1(1/5 - 1/6 +1/6-1/7+ 1/7 - 1/8 +...+1/2016 - 1/2017)
= 1(1/5 - 1/2017)
= 1.2012/10085
= 2012/10085
1/5.6 - 1/6.7 - 1/7.8 - ... 1/2016.2017
= 1 ( 1/5 - 1/6 - 1/7 - 1/8 + ... + 1/2016 - 1/2017 )
= 1 ( 1/5 - 1/2017 )
= 1.2012/10085
= 2012/10085