C =\(70\left(\dfrac{131313}{565656}+\dfrac{131313}{727272}+\dfrac{131313}{909090}\right)\)
K
Khách
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26 tháng 9 2021
b: Ta có: \(B=\dfrac{1}{4\cdot9}+\dfrac{1}{9\cdot14}+...+\dfrac{1}{64\cdot69}\)
\(=\dfrac{1}{5}\left(\dfrac{5}{4\cdot9}+\dfrac{5}{9\cdot14}+...+\dfrac{5}{64\cdot69}\right)\)
\(=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{14}+...+\dfrac{1}{64}-\dfrac{1}{69}\right)\)
\(=\dfrac{1}{5}\cdot\dfrac{65}{4\cdot69}\)
\(=\dfrac{13}{276}\)
26 tháng 9 2021
\(A=\dfrac{2}{1\cdot4}+\dfrac{2}{4\cdot7}+...+\dfrac{2}{97\cdot100}\\ A=\dfrac{2}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{97\cdot100}\right)\\ A=\dfrac{2}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\\ A=\dfrac{2}{3}\left(1-\dfrac{1}{100}\right)=\dfrac{2}{3}\cdot\dfrac{99}{100}=\dfrac{33}{50}\\ B=\dfrac{1}{4\cdot9}+\dfrac{1}{9\cdot14}+...+\dfrac{1}{64\cdot69}\\ B=\dfrac{1}{5}\left(\dfrac{5}{4\cdot9}+\dfrac{5}{9\cdot14}+...+\dfrac{5}{64\cdot69}\right)\\ B=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{14}+...+\dfrac{1}{64}-\dfrac{1}{69}\right)\\ B=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{69}\right)=\dfrac{1}{5}\cdot\dfrac{65}{276}=\dfrac{13}{276}\)
\(C=70\left(\dfrac{13}{56}+\dfrac{13}{72}+\dfrac{13}{90}\right)=70\cdot13\left(\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\right)\\ C=910\left(\dfrac{1}{7\cdot8}+\dfrac{1}{8\cdot9}+\dfrac{1}{9\cdot10}\right)\\ C=910\left(\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\right)\\ C=910\left(\dfrac{1}{7}-\dfrac{1}{10}\right)=910\cdot\dfrac{3}{70}=39\)
22 tháng 5 2019
\(B=70.\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
\(B=70.\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
\(B=70.13.\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)
\(B=910.\left(\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(B=910.\left(\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
\(B=910.\left[\frac{1}{7}+\left(\frac{1}{8}-\frac{1}{8}\right)+\left(\frac{1}{9}-\frac{1}{9}\right)-\frac{1}{10}\right]\)
\(B=910.\left[\frac{1}{7}-\frac{1}{10}\right]\)
\(B=910.\frac{3}{70}=39\)
~ Hok tốt ~
NN
2
PQ
2
DA
12 tháng 3 2020
\(B=70\cdot\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
\(B=70\cdot\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
\(B=70\cdot\frac{39}{70}\)
\(B=39\)
Vậy B = 39
12 tháng 3 2020
B=\(70\times\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
B=\(70\times\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
B=\(70\times\frac{39}{70}\)
B=\(39\)
Nếu mk làm sai thì xin lỗi bạn nhiều nha
OS
7
29 tháng 3 2016
B=70.\(\left(\frac{13.10101}{56.10101}+\frac{13.10101}{72.10101}+\frac{13.10101}{90.10101}\right)\)
B=70.\(\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
B=70.\(\frac{39}{70}\)=39
ks nha
29 tháng 3 2016
B= 70.( 131313/565656 + 131313/727272 + 131313/909090)
B = 70 * ( 13/56 + 13/72 + 13/90)
B = 70* 0,1464....
B= 10,254050...
13 tháng 2 2020
\(B=70\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
\(B=70\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
\(B=70.13\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)
\(B=70.13.\frac{3}{70}\)
\(B=39\)
13 tháng 2 2020
\(B=70\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
\(=70\left(\frac{13.10101}{56.10101}+\frac{13.10101}{72.10101}+\frac{13.10101}{90.10101}\right)\)
\(=70\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)
\(=70.13\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)
\(=910\left(\frac{45}{2520}+\frac{35}{2520}+\frac{28}{2520}\right)\)
\(=910.\frac{3}{70}\)
\(=39\)
Vậy \(B=39\)
D
25 tháng 4 2017
Ta có: \(\frac{131313}{565656}=\frac{131313:10101}{565656:10101}=\frac{13}{56}\)
\(\frac{131313}{727272}=\frac{13}{72}\)
\(\frac{131313}{909090}=\frac{13}{90}\)
\(\Rightarrow C=70\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)=70\left(\frac{39}{79}\right)=39\)
Vậy C = 39
25 tháng 4 2017
C=70(\(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\))=70\(\frac{39}{70}\)=39
\(C=70.\left(131313.\left(\dfrac{1}{565656}+\dfrac{1}{727272}+\dfrac{1}{909090}\right)\right)\)
\(C=70.\left(131313.\dfrac{1}{235690}\right)\)
\(C=70.\dfrac{39}{70}\)
\(C=39\)