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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
NT
5
8 tháng 11 2019
\(A=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(=\frac{1}{11}-\frac{1}{66}=\frac{5}{66}\)
8 tháng 11 2019
\(A=\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\)
\(A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\)
\(A=\frac{1}{11}-\frac{1}{66}\)
\(A=\frac{6}{66}-\frac{1}{66}\)
\(A=\frac{5}{66}\)
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
\(A=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=5.\left(\frac{1}{11.16}+\frac{1}{16.21}+...+\frac{1}{61.66}\right)\)
\(=5.\frac{1}{4}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{24}+...+\frac{1}{61}-\frac{1}{66}\right)\)
\(=\frac{5}{4}.\left(\frac{1}{11}-\frac{1}{66}\right)\)
\(=\frac{5}{4}.\frac{5}{66}\)
\(=\frac{25}{264}\)
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_
11 tháng 3 2020
\(D=\frac{3}{11\cdot16}+\frac{3}{16\cdot21}+\frac{3}{21\cdot26}+....+\frac{3}{61\cdot66}\)
\(\frac{5}{3}D=\frac{5}{3}\left(\frac{3}{11\cdot16}+\frac{3}{16\cdot21}+\frac{3}{21\cdot26}+.....+\frac{3}{61\cdot66}\right)\)
\(\frac{5}{3}D=\frac{5}{11\cdot16}+\frac{5}{16\cdot21}+\frac{5}{21\cdot26}+....+\frac{5}{61\cdot66}\)
\(\frac{5}{3}D=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+....+\frac{1}{61}-\frac{1}{66}\)
\(\frac{5}{3}D=\frac{1}{11}-\frac{1}{66}\)
\(\frac{5}{3}D=\frac{5}{66}\)
\(D=\frac{5}{66}:\frac{5}{3}=\frac{5}{66}\cdot\frac{6}{5}=\frac{1}{11}\)
E
11 tháng 3 2020
D = 3/11.16 + 3/16.21 + 3/21.26 + ...... + 3/61.66
D = \(\frac{3}{5}\) . ( \(\frac{5}{11.16}\)+ \(\frac{5}{16.21}\)+......+\(\frac{5}{61.66}\) )
D = \(\frac{3}{5}\). ( \(\frac{1}{11}\)- \(\frac{1}{16}\) + \(\frac{1}{16}\)- \(\frac{1}{21}\)+ ......... + \(\frac{1}{61}\)- \(\frac{1}{66}\))
D =\(\frac{3}{5}\). ( \(\frac{1}{11}\)- \(\frac{1}{66}\))
D = \(\frac{3}{5}\). \(\frac{5}{66}\)
D = \(\frac{1}{22}\)
# HOK TỐT #
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^^
LD
1
11 tháng 4 2018
Ta có :
\(A=\frac{5^2}{6.11}+\frac{5^2}{11.16}+\frac{5^2}{16.21}+...+\frac{5^2}{91.96}\)
\(A=5\left(\frac{5}{6.11}+\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{91.96}\right)\)
\(A=5\left(\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{91}-\frac{1}{96}\right)\)
\(A=5\left(\frac{1}{6}-\frac{1}{96}\right)\)
\(A=5.\frac{5}{32}\)
\(A=\frac{25}{32}\)
Vậy \(A=\frac{25}{32}\)
Chúc bạn học tốt ~
7 tháng 8 2016
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{99\cdot100}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
\(=>A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(=>A=\frac{1}{11}-\frac{1}{66}\)
\(=>A=\frac{5}{66}\)
li ke nha
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