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Câu hỏi của Lê Thúy Hằng - Toán lớp 6 | Học trực tuyến

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\(B=1-\frac{1}{2.5}+1-\frac{1}{5.8}+...+1-\frac{1}{50.53}\) 

\(B=17-\frac{1}{3}\left(\frac{3}{2.5}+\frac{3}{5.8}+....+\frac{3}{50.53}\right)\) 

\(B=17-\frac{1}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-.....-\frac{1}{53}\right)\) 

\(B=17-\frac{1}{3}\left(\frac{1}{2}-\frac{1}{53}\right)=17-\frac{1}{3}.\frac{51}{106}=17-\frac{17}{106}=17\left(1-\frac{1}{106}\right)=17.\frac{105}{106}=\frac{1785}{106}\)

B=9/2,5+39/5,8+87/8,11+...+2649/50,53

B=2,5-1/2,5+5,8-1/5,8+8,11-1/8,11+...+50,53-1/50,53

B=1-1/2,5+1-1/5,8+1-1/8,11+...+1-1/50,53

B=17-1/3(3/2,5+3/5,8+3/8,11+...+3/50,53

B=17-1/3(1/2-1/5+1/5-1/8+...+1/50-1/53)

B=17-1/3(1/2-1/53)

B=1785/106

Học tốt nha bạn ~!!!

Câu hỏi của Lê Thúy Hằng - Toán lớp 6 | Học trực tuyến

Đề hình như bị sai ban ơi sửa lại

\(A=\dfrac{3}{2.5}+\dfrac{3}{5.8}+\dfrac{3}{8.11}+...+\dfrac{3}{92.95}\)

\(A=3\left(\dfrac{1}{2.5}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+...+\dfrac{1}{92.95}\right)\)

\(A=3.\dfrac{1}{3}\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{92}-\dfrac{1}{95}\right)\)

\(A=\dfrac{1}{2}-\dfrac{1}{95}\)

\(A=\dfrac{93}{190}\)

\(B=\dfrac{2}{2.5}+\dfrac{2}{5.8}+\dfrac{2}{8.11}+...+\dfrac{2}{92.95}\)

\(3B=2\left(\dfrac{1}{2.5}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+...+\dfrac{1}{92.95}\right)\)

\(3B=2.\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{92}-\dfrac{1}{95}\right)\)

\(3B=2\left(\dfrac{1}{2}-\dfrac{1}{95}\right)\)

\(3B=2.\dfrac{93}{190}\)

\(3B=\dfrac{93}{95}\)

\(\Rightarrow B=\dfrac{31}{95}\)

=21​−51​+51​−71​+....+951​−981​

=12−198=21​−981​tự làm tiếp

A = 1/2.5 + 1/5.8 + 1/8.11 + ... + 1/92.95 + 1/95.98

A = 1/3 . ( 3/2.5 + 3/5.8 + 3/8.11 + ... + 3/92.95 + 3/95.98 )

A = 1/3 . ( 1/2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/11 + ... + 1/92 - 1/95 + 1/95 - 1/98 )

A = 1/3 . ( 1/2 - 1/98 )

A = 1/3 . 24/49

A = 8/49 tick cho tui

=1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/14

=1/2-1/14

=7/14-1/14=6/14=3/7

 bằng 3.141939849 kết bạn với mình nhé

Ta có : B = 4 / 2. 5 + 4 / 5 . 8 + 4 / 8 . 11 + 4 / 11 . 14

               = 4 ( 1 / 2 . 5 + 1 / 5 . 8 + 1 / 8 . 11 + 1 / 11 . 14 )

              = 4 . [ 1/3 ( 1 /2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/ 11 + 1/11 - 1/14 )]

              = 4 / 3 ( 1/ 2 - 1/14 )

             = 4/3 . 3/7

             = 4 / 7 

Vậy B = 4 / 7 

B = \(\frac{4}{2\times5}+\frac{4}{5\times8}+\frac{4}{8\times11}+\frac{4}{11\times14}\)

B = \(\frac{4}{10}+\frac{4}{40}+\frac{4}{88}+\frac{4}{154}\)

B = \(\frac{1}{73}\)\(\left(\frac{4}{292}\right)\)

\(A=\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{2015.2018}\)

\(=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{2015}-\frac{1}{2018}\)

\(=\frac{1}{2}-\frac{1}{2018}=\frac{504}{1009}\)

Vậy \(A=\frac{504}{1009}.\)

\(B=\frac{4}{2.6}+\frac{4}{6.10}+\frac{4}{10.14}+...+\frac{4}{102.106}\)

\(=\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{102}-\frac{1}{106}\)

\(=\frac{1}{2}-\frac{1}{106}=\frac{26}{53}\)

Vậy \(B=\frac{26}{53}.\)

Bài làm:

a) \(A=\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{2015.2018}\)

\(A=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{2015}-\frac{1}{2018}\)

\(A=\frac{1}{2}-\frac{1}{2018}\)

\(A=\frac{504}{1009}\)

b) \(B=\frac{4}{2.6}+\frac{4}{6.10}+\frac{4}{10.14}+...+\frac{4}{102.106}\)

\(B=\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{102}-\frac{1}{106}\)

\(B=\frac{1}{2}-\frac{1}{106}\)

\(B=\frac{26}{53}\)

\(A=\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{2015.2018}=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{2015}-\frac{1}{2018}\)

\(=\frac{1}{2}-\frac{1}{2018}=\frac{504}{1009}\)

\(B=\frac{4}{2.6}+\frac{4}{6.10}+...+\frac{4}{102.106}=\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+...+\frac{1}{102}-\frac{1}{106}=\frac{1}{2}-\frac{1}{106}\)

\(=\frac{26}{53}\)

nhầm : 51/310

   1/2.5+1/5.8+1/8.11+...+1/152.155

=1/3(3/2.5+3/5.8+3/8.11+...+3/152.155

=1/3(1/2-1/5+1/5-1/8+1/8-1/11+...+1/152-1/155)

=1/3(1/2-1/155)

=1/3(155/310-2/310)

=1/3.153/310=51/310

Kết quả:51/310