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15 tháng 5 2016

\(B=7\left(\frac{5}{2.1}+\frac{4}{1.11}+...+\frac{13}{15.4}\right)\)

\(B=7\left(\frac{5}{2.7}+\frac{4}{7.11}+...+\frac{13}{15.28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{28}\right)\)

\(B=7\times\frac{13}{28}\)

\(B=\frac{13}{4}\)

4 tháng 5 2017

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(=\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)

\(=\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)

\(=\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)

\(=\frac{B}{7}=\frac{13}{28}\)

\(=B=\frac{13}{28}.7\)

\(=B=\frac{13}{4}\)

23 tháng 5 2016

\(\frac{1}{7}\)B=\(\frac{5}{2.7.1}+\frac{4}{1.7.11}+\frac{3}{11.2.7}+\frac{1}{2.7.15}+\frac{13}{15.4.7}\)

\(\frac{1}{7}\)B=\(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)

\(\frac{1}{7}B=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(\frac{1}{7}B=\frac{1}{2}-\frac{1}{28}\)

\(\frac{1}{7}B=\frac{13}{28}\)

B=\(\frac{13}{28}:\frac{1}{7}\)

B=\(\frac{13}{4}\)

1 tháng 5 2019

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

1717B=52.7.1+41.7.11+311.2.7+12.7.15+1315.4.752.7.1+41.7.11+311.2.7+12.7.15+1315.4.7

1717B=52.7+47.11+311.14+114.15+1315.2852.7+47.11+311.14+114.15+1315.28

17B=12−17+17−111+111−114+114−115+115−12817B=12−17+17−111+111−114+114−115+115−128

17B=12−12817B=12−128

17B=132817B=1328

B=1328:171328:17

B=134

15 tháng 5 2016

Ta có : 

\(B=\frac{5}{2\cdot1}+\frac{4}{1\cdot11}+\frac{3}{11\cdot2}+\frac{1}{2\cdot15}+\frac{13}{15\cdot4}\)

\(=>\frac{B}{7}=\frac{5}{2\cdot7}+\frac{4}{7\cdot11}+\frac{3}{11\cdot14}+\frac{1}{14\cdot15}+\frac{13}{15\cdot28}\)

\(=>\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(=>\frac{B}{7}=\frac{1}{2}-\frac{1}{28}=\frac{14}{28}-\frac{1}{28}=\frac{13}{28}\)

\(=>B=\frac{13}{28}\cdot7=\frac{13}{4}\)

15 tháng 5 2016

Khó wá

10 tháng 8 2015

B = \(\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

B = \(7.\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)

B = \(7.\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

B = \(7.\left(\frac{1}{2}-\frac{1}{28}\right)\)

B = \(7.\frac{13}{28}\)

B = \(\frac{13}{4}\)

4 tháng 3 2017

cho mình hỏi viết phân số kiểu gì zợ?

15 tháng 2 2017

\(\frac{13}{4}\)

15 tháng 2 2017

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(\Rightarrow\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)

\(\Rightarrow\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(\Rightarrow\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)

\(\Rightarrow\frac{B}{7}=\frac{14}{28}-\frac{1}{28}\)

\(\Rightarrow\frac{B}{7}=\frac{13}{28}\)

\(\Rightarrow B=\frac{13}{28}.7\)

\(\Rightarrow B=\frac{13}{4}\)

4 tháng 4 2016

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(B:7=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{28} \)

\(\frac{B}{7}=\frac{13}{28}\)

B=\(\frac{13}{28}\cdot7\)

B=\(\frac{13}{4}\left(=3\frac{1}{4}\right)\)

4 tháng 4 2016

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)

\(\frac{B}{7}=\frac{13}{28}\)

\(B=\frac{13}{4}\left(=3\frac{1}{4}\right)\)

18 tháng 5 2018

Trả lời:

\(\frac{5}{2\cdot1}+\frac{4}{1\cdot11}+\frac{3}{11\cdot2}+\frac{1}{2\cdot15}\)\(+\frac{13}{15\cdot4}\)

\(=\frac{5}{2}+\frac{4}{11}+\frac{3}{22}+\frac{1}{30}\)\(+\frac{13}{60}\)

\(=\frac{55+8+3}{22}\)\(+\frac{2+13}{60}\)

\(=\frac{66}{22}\)\(+\frac{1}{4}\)

\(=\frac{13}{4}\)

Hc tốt #

9 tháng 3 2017

\(B=\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}+\dfrac{13}{15.4}\)

\(\dfrac{B}{7}=\dfrac{5}{2.7}+\dfrac{4}{7.11}+\dfrac{3}{11.14}+\dfrac{1}{14.15}+\dfrac{13}{15.4}\)

\(\dfrac{B}{7}=\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{7}{11}+...+\dfrac{1}{15}-\dfrac{1}{28}\)

\(\dfrac{B}{7}=\dfrac{1}{2}-\dfrac{1}{28}\)

\(\dfrac{B}{7}=\dfrac{13}{28}\)

\(B=\dfrac{13}{28}.7=\dfrac{13}{4}\)

29 tháng 7 2017

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{2}{2.15}+\frac{13}{15.4}\)

\(B=\frac{1}{2}-1+1-\frac{1}{11}+\frac{1}{11}-\frac{1}{2}+\frac{1}{2}-\frac{1}{15}+\frac{1}{15}-\frac{1}{4}\)

\(B=\frac{1}{2}-\frac{1}{4}\)

\(B=\frac{1}{4}\)

29 tháng 7 2017

đáp án là:1/4