HH
1
K
Khách
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DH
1
N
17 tháng 4 2016
\(32\left(\frac{1}{8.11}+\frac{1}{11.14}+\frac{1}{14.17}+...+\frac{1}{197.200}\right)-x=\frac{1}{2}\)
\(\frac{32}{3}\left(\frac{3}{8.11}+\frac{3}{11.14}+\frac{3}{14.17}+....+\frac{3}{197.200}\right)-x=\frac{1}{2}\)
\(\frac{32}{3}\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+...+\frac{1}{197}-\frac{1}{200}\right)-x=\frac{1}{2}\)
\(\frac{32}{3}\left(\frac{1}{8}-\frac{1}{200}\right)-x=\frac{1}{2}\)
x=0.78
HH
1
5 tháng 4 2019
\(B=\frac{9}{8\cdot11}+\frac{9}{11\cdot14}+...+\frac{9}{197\cdot200}\)
\(=3\left(\frac{3}{8\cdot11}+\frac{3}{11\cdot14}+...+\frac{3}{197\cdot200}\right)\)
\(=3\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{197}-\frac{1}{200}\right)\)
\(=3\left(\frac{1}{8}-\frac{1}{200}\right)\)
\(=3\left(\frac{24}{200}-\frac{1}{200}\right)\)
\(=3\cdot\frac{23}{200}\)
đúng
LN
1
NM
3
OY
28 tháng 7 2021
\(\dfrac{3^2}{8.11}+\dfrac{3^2}{11.14}+...+\dfrac{3^2}{197.200}\)
=\(3.\left(\dfrac{3}{8.11}+\dfrac{3}{11.14}+...+\dfrac{3}{197.200}\right)\)
=\(3.\left(\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}+...+\dfrac{1}{197}-\dfrac{1}{200}\right)\)
=\(3.\left(\dfrac{1}{8}-\dfrac{1}{200}\right)\)
=\(3.\dfrac{3}{25}=\dfrac{9}{25}\)
AC
3
15 tháng 2 2016
N=3(3/8.11 +3 /11.14 + 3/14.17 +...+3/197.200)
N=3( 1/8-1/11+1/11-1/14+1/14-1/17+...+1/197-1/200)
N=3(1/8-1/200)
N=3. 3/25=9/25
Ủng hộ mk nha
15 tháng 2 2016
\(\Rightarrow N=\frac{9}{8.11}+\frac{9}{11.14}+\frac{9}{14.17}+....+\frac{9}{197.200}\)
\(\Rightarrow N=\frac{9}{3}\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{197}-\frac{1}{200}\right)\)
\(\Rightarrow N=3\left(\frac{1}{8}-\frac{1}{200}\right)=\frac{3}{8}-\frac{3}{200}=\frac{75}{200}-\frac{3}{200}=\frac{72}{200}=\frac{9}{25}\)
25 tháng 3 2017
a, Ta có :
\(C=\dfrac{7}{10.11}+\dfrac{7}{11.12}+.......+\dfrac{7}{69.70}\)
\(=7\left(\dfrac{1}{10.11}+\dfrac{1}{11.12}+.........+\dfrac{1}{69.70}\right)\)
= \(7\left(\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}+........+\dfrac{1}{69}-\dfrac{1}{70}\right)\)
= \(7\left(\dfrac{1}{10}-\dfrac{1}{70}\right)=7.\dfrac{6}{70}=\dfrac{3}{5}\)
b, \(E=\dfrac{3^2}{8.11}+\dfrac{3^2}{11.14}+........+\dfrac{3^2}{197.200}\)
\(=3.\left(\dfrac{3}{8.11}+\dfrac{3}{11.14}+......+\dfrac{3}{197.200}\right)\)
= \(3.\left(\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}+......+\dfrac{1}{197}-\dfrac{1}{200}\right)\)
= \(3.\left(\dfrac{1}{8}-\dfrac{1}{200}\right)=3.\dfrac{24}{200}=\dfrac{9}{25}\)
KN
26 tháng 2 2019
Đặt \(A=\frac{3^2}{8.11}+\frac{3^2}{11.14}+\frac{3^2}{14.17}+...+\frac{3^2}{197.200}\)
\(\Leftrightarrow A=\frac{9}{8.11}+\frac{9}{11.14}+\frac{9}{14.17}+...+\frac{9}{197.200}\)
\(\Leftrightarrow\frac{1}{3}A=\frac{3}{8.11}+\frac{3}{11.14}+\frac{3}{14.17}+...+\frac{3}{197.200}\)
\(\Leftrightarrow\frac{1}{3}A=\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{2}{17}+...+\frac{1}{197}-\frac{1}{200}\)b
\(\Leftrightarrow\frac{1}{3}A=\frac{1}{8}-\frac{1}{200}\)
\(\Leftrightarrow\frac{1}{3}A=\frac{24}{200}\)
\(\Leftrightarrow A=\frac{24}{200}\times3\)
\(\Leftrightarrow A=\frac{72}{200}=\frac{9}{25}\)
Ta có :
\(C=\frac{3^2}{8.11}+\frac{3^2}{11.14}+\frac{3^2}{14.17}+...+\frac{3^2}{197.200}\)
\(C=3\left(\frac{3}{8.11}+\frac{3}{11.14}+\frac{3}{14.17}+...+\frac{3}{197.200}\right)\)
\(C=3\left(\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+...+\frac{1}{197}-\frac{1}{200}\right)\)
\(C=3\left(\frac{1}{8}-\frac{1}{200}\right)\)
\(C=3.\frac{3}{25}\)
\(C=\frac{9}{25}\)
Chúc bạn học tốt ~