LV
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K
Khách
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TV
1
2 tháng 4 2015
S:5=\(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{21.26}\)
S:5=\(\frac{6-1}{1.6}+\frac{11-6}{6.11}+...+\frac{26-21}{21.26}\)
S:5=\(\frac{6}{1.6}-\frac{1}{1.6}+\frac{11}{6.11}-\frac{6}{6.11}+...+\frac{26}{21.26}-\frac{21}{21.26}\)
S:5=1-\(\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+....+\frac{1}{21}-\frac{1}{26}\)
S:5=1-\(\frac{1}{26}\)
S:5=\(\frac{25}{26}\)
S=\(\frac{25}{26}.5\)
S=\(\frac{125}{26}\)
BQ
1
11 tháng 5 2018
Ta có : \(\frac{5^2}{1.6}+\frac{5^2}{6.11}+\frac{5^2}{11.16}+.....+\frac{5^2}{26.31}\)
\(=5\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+....+\frac{5}{26.31}\right)\)
\(=5\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+....+\frac{1}{26}-\frac{1}{31}\right)\)
\(=5\left(1-\frac{1}{31}\right)=5.\frac{30}{31}=\frac{150}{31}\)
S
11 tháng 3 2017
A = \(\frac{2}{1.4}+\frac{2}{4.7}+...+\frac{2}{97.100}\)
= \(\frac{2}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{100}\right)\)
= \(\frac{2}{3}\left(1-\frac{1}{100}\right)\)
= \(\frac{2}{3}.\frac{99}{100}=\frac{33}{50}\)
B = \(\frac{5^2}{1.6}+\frac{5^2}{6.11}+\frac{5^2}{11.16}+\frac{5^2}{16.21}+\frac{5^2}{16.21}+\frac{5^2}{21.26}+\frac{5^2}{26.31}\)
= \(5\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+\frac{5}{26.31}\right)\)
= \(5.\frac{5}{5}.\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+\frac{1}{26}-\frac{1}{31}\right)\)
= \(5\left(1-\frac{1}{31}\right)\)
= \(5.\frac{30}{31}=\frac{150}{31}\)
NN
1
LM
Lê Minh Vũ
CTVHS
23 tháng 2 2022
\(A=\frac{5^2}{1.6}+\frac{5^2}{6.11}+\frac{5^2}{11.16}+\frac{5^2}{16.21}+\frac{5^2}{21.26}+\frac{5^2}{26.31}\)
\(\frac{A}{5}=\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+\frac{5}{26.31}\)
\(\frac{A}{5}=1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+\frac{1}{26}-\frac{1}{31}\)
\(\frac{A}{5}=1-\frac{1}{31}\)
\(A=\frac{150}{31}\)
PT
4
21 tháng 3 2017
M = \(\frac{1}{2}\)+ \(\frac{1}{6}\)+ \(\frac{1}{12}\)+ \(\frac{1}{20}\)+ \(\frac{1}{30}\)+ \(\frac{1}{42}\)
= \(\frac{6}{7}\)
TT
1
VT
24 tháng 4 2017
C=5(5/1.6+5/6.11+...+5/26.31)
C=5(1-1/6+1/6-1/11+...+1/26-1/31)
C=5(1-1/31)
C=5.30/31
C=150/31
CHÚC BẠN HỌC TỐT!!!
NN
1
11 tháng 4 2018
Ta có :
\(\frac{5^2}{1.6}+\frac{5^2}{6.11}+\frac{5^2}{11.16}+...+\frac{5^2}{46.51}\)
\(=\)\(5\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{5}{46.51}\right)\)
\(=\)\(5\left(\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{46}-\frac{1}{51}\right)\)
\(=\)\(5\left(1-\frac{1}{51}\right)\)
\(=\)\(5.\frac{50}{51}\)
\(=\)\(\frac{250}{51}\)
Chúc bạn học tốt ~
DT
0
\(\frac{5^2}{1.6}+\frac{5^2}{6.11}+\frac{5^2}{11.16}+\frac{5^2}{16.21}+\frac{5^2}{21.26}\)
= \(5\left(\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}\right)\)
=\(5\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}\right)\)=\(5\left(1-\frac{1}{26}\right)\)
=\(5.\frac{25}{26}\)
=\(\frac{125}{26}\)