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ML
4 tháng 5 2017
\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
\(=\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)
\(=\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)
\(=\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)
\(=\frac{B}{7}=\frac{13}{28}\)
\(=B=\frac{13}{28}.7\)
\(=B=\frac{13}{4}\)
GV
1
26 tháng 2 2016
Ta có
\(10=2.5\)
\(24=2^3.3\)
\(56=2^3.7\)
MC:\(2^3.3.5.7=840\)
QĐ:\(-\frac{3}{10}=\frac{-252}{840};\frac{5}{24}=\frac{175}{840};\frac{-21}{56}=\frac{-315}{840}\)
Ủng hộ cho mình nha bạn
20 tháng 6 2021
Giải:
\(\dfrac{3}{2}+\dfrac{6}{8}+\dfrac{9}{28}+\dfrac{12}{77}+\dfrac{15}{176}\)
\(=\dfrac{3}{1.2}+\dfrac{6}{2.4}+\dfrac{9}{4.7}+\dfrac{12}{7.11}+\dfrac{15}{11.16}\)
\(=3.\left(\dfrac{1}{1.2}+\dfrac{2}{2.4}+\dfrac{3}{4.7}+\dfrac{4}{7.11}+\dfrac{5}{11.16}\right)\)
\(=3.\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}\right)\)
\(=3.\left(1-\dfrac{1}{16}\right)\)
\(=3.\dfrac{15}{16}\)
\(=\dfrac{45}{16}\)
20 tháng 6 2021
Đặt A = \(\dfrac{3}{2}+\dfrac{6}{8}+\dfrac{9}{28}+\dfrac{12}{77}+\dfrac{15}{176}\)
= \(3\left(\dfrac{1}{1\times2}+\dfrac{2}{2\times4}+\dfrac{3}{4\times7}+\dfrac{4}{7\times11}+\dfrac{5}{11\times16}\right)\)
= \(3\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}\right)\)
= \(3\left(1-\dfrac{1}{16}\right)=3\times\dfrac{15}{16}=\dfrac{45}{16}\)
19 tháng 11 2021
\(a,\Rightarrow A=-1\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{9.10}\right)\)
\(\Rightarrow A=-1\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\)
\(\Rightarrow A=-1\left(\dfrac{1}{4}-\dfrac{1}{10}\right)\)
\(\Rightarrow A=\dfrac{-3}{20}\)
19 tháng 11 2021
Bài 2:
\(a,\dfrac{1717}{8585}=\dfrac{1717:1717}{8585:1717}=\dfrac{1}{5};\dfrac{1313}{5151}=\dfrac{1313:101}{5151:101}=\dfrac{13}{51}\\ \dfrac{1}{5}=\dfrac{51}{255}< \dfrac{65}{255}=\dfrac{13}{51}\\ \Rightarrow\dfrac{1717}{8585}< \dfrac{1313}{5151}\)
\(b,\dfrac{201201}{202202}=\dfrac{201201:1001}{202202:1001}=\dfrac{201}{202}=\dfrac{201\cdot1001001}{202\cdot1001001}=\dfrac{201201201}{202202202}\)
tôi thức
\(\frac{3}{8}=\frac{3.27}{8.27}=\frac{81}{216}\)
\(\frac{5}{27}=\frac{5.8}{27.8}=\frac{40}{216}\)
MCS: 216
\(\frac{3}{8}\)=\(\frac{3.27}{8.27}\)=\(\frac{81}{216}\) ; \(\frac{5}{27}\)=\(\frac{5.8}{27.8}\)=\(\frac{40}{216}\)