\(B=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
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DN
4
19 tháng 2 2017
\(A=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(=\frac{1}{11}-\frac{1}{66}\)
\(=\frac{5}{66}\)
Vậy \(A=\frac{5}{66}\)
19 tháng 2 2017
\(A=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=5.\left(\frac{1}{11.16}+\frac{1}{16.21}+...+\frac{1}{61.66}\right)\)
\(=5.\frac{1}{4}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{24}+...+\frac{1}{61}-\frac{1}{66}\right)\)
\(=\frac{5}{4}.\left(\frac{1}{11}-\frac{1}{66}\right)\)
\(=\frac{5}{4}.\frac{5}{66}\)
\(=\frac{25}{264}\)
FT
14 tháng 11 2017
\(B=\dfrac{5}{11.16}+\dfrac{5}{16.21}+...+\dfrac{5}{61.66}\)
\(B=\dfrac{5}{5}\left(\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{21}+...+\dfrac{1}{61}-\dfrac{1}{66}\right)\)
\(B=\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{21}+...+\dfrac{1}{61}-\dfrac{1}{66}\)
\(B=\dfrac{1}{11}-\dfrac{1}{66}\)
\(B=\dfrac{6}{66}-\dfrac{1}{66}=\dfrac{5}{66}\)
PH
7
MT
23 tháng 6 2015
\(\frac{1}{11.16}+\frac{1}{16.21}+\frac{1}{21.26}+...+\frac{1}{61.66}\)
=\(\frac{1}{5}.\frac{5}{11.16}+\frac{1}{5}.\frac{5}{16.21}+\frac{1}{5}.\frac{5}{21.26}+...+\frac{1}{5}.\frac{5}{61.66}\)
=\(\frac{1}{5}.\left(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\right)\)
=\(\frac{1}{5}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\right)\)
=\(\frac{1}{5}.\left(\frac{1}{11}-\frac{1}{66}\right)\)
=\(\frac{1}{5}.\left(\frac{6}{66}-\frac{1}{66}\right)=\frac{1}{5}.\frac{5}{66}=\frac{1}{66}\)
23 tháng 6 2015
Đặt A = \(\frac{1}{11.16}+...+\frac{1}{61.66}\)
5A = \(\frac{5}{11.16}+..+\frac{5}{61.66}\)
5a = \(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
5a = \(\frac{1}{11}-\frac{1}{61}\)
5a = 50/671
a = \(\frac{50}{671}:5=\frac{10}{671}\)
1 tháng 12 2019
a, \(A=\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\)
\(A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\)
\(A=\frac{1}{11}-\frac{1}{66}\)
\(A=\frac{5}{66}\)
b, \(B=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)
\(B=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\)
\(B=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)
\(B=1-\frac{1}{7}\)
\(B=\frac{6}{7}\)
_Học tốt nha_
25 tháng 3 2015
A=\(\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
A=\(\left(\frac{1}{11}-\frac{1}{16}\right)+\left(\frac{1}{16}-\frac{1}{21}\right)+...+\left(\frac{1}{61}-\frac{1}{66}\right)\)
A=\(\frac{1}{11}+\left(\left(\frac{1}{16}-\frac{1}{16}\right)+\left(\frac{1}{21}-\frac{1}{21}\right)+...+\left(\frac{1}{61}-\frac{1}{61}\right)\right)-\frac{1}{66}\)
A=\(\frac{1}{11}+0-\frac{1}{66}\)
A=\(\frac{5}{66}\)
25 tháng 3 2015
A=11-16\11.16+21-16\21.16+...+66-61\61.66
A=1\11-1\16+1\16-...-1\66
A=1\11-1\66
A=5\66
nếu đúng thì like nhé
7 tháng 8 2016
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{99\cdot100}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
18 tháng 10 2015
\(=>A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(=>A=\frac{1}{11}-\frac{1}{66}\)
\(=>A=\frac{5}{66}\)
li ke nha
18 tháng 10 2015
A= 5/11.16 + 5/16.21 + .....+5/61.66
A = 1/5.(5/11 - 5/16 + 5/16 - .......5/66)
A = 1/5 . 25/66 = 5/66
22 tháng 11 2017
a/ \(A=\frac{1}{6}+\frac{1}{12}+.........+\frac{1}{56}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+..........+\frac{1}{7.8}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.........+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{2}-\frac{1}{8}=\frac{3}{4}\)
b/ \(B=\frac{5}{11.16}+\frac{5}{16.21}+........+\frac{5}{61.66}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+........+\frac{1}{61}-\frac{1}{66}\)
\(=\frac{1}{11}-\frac{1}{66}\)
\(=\frac{5}{66}\)
22 tháng 11 2017
a) \(A=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}\)
\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(A=\frac{1}{2}-\frac{1}{8}=\frac{3}{8}\)
b) \(B=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(B=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(B=\frac{1}{11}-\frac{1}{66}=\frac{5}{66}\)
DS
13 tháng 7 2016
\(A=5.\left(\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{56.61}\right)\))
\(A=5.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{56}-\frac{1}{61}\right)\)
\(A=5.\left(\frac{1}{11}-\frac{1}{61}\right)\)
\(A=5.\frac{50}{671}\)
\(A=\frac{250}{671}\)
Chúc em học tốt^^
\(\frac{5}{66}\) nha
\(B=\frac{5}{11.13}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(\Rightarrow B=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(\Rightarrow B=\frac{1}{11}-\frac{1}{66}\)
\(\Rightarrow B=\frac{5}{66}\)