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a)\(\frac{4}{3.7}+\frac{4}{7.11}+...+\frac{4}{23.27}=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{23}-\frac{1}{27}=\frac{1}{3}-\frac{1}{27}=\frac{8}{27}\)
b)\(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{6.7}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{6}-\frac{1}{7}=\frac{1}{2}-\frac{1}{7}=\frac{5}{14}\)
c)\(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{11.13}+\frac{2}{1.2}+\frac{2}{2.3}+...+\frac{2}{9.10}=\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\right)+2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\frac{1}{3}-\frac{1}{13}+2\left(1-\frac{1}{10}\right)=\frac{10}{39}+\frac{9}{5}=\frac{401}{195}\)
\(\left(6\div\dfrac{3}{5}-1\dfrac{1}{6}\times\dfrac{6}{7}\right)\div\left(4\dfrac{1}{5}\times\dfrac{10}{11}+5\dfrac{2}{11}\right)\)
\(=\left(6\times\dfrac{5}{3}-\dfrac{7}{6}\times\dfrac{6}{7}\right)\div\left(\dfrac{21}{5}\times\dfrac{10}{11}+\dfrac{57}{11}\right)\)
\(=\left(10-1\right)\div\left(\dfrac{210}{55}+\dfrac{57}{11}\right)\)
\(=9\div9\)
\(=1\)
\(\frac{5}{11}+\frac{1}{14}+\frac{2}{5}+\frac{6}{11}+\frac{3}{4}+\frac{6}{25}+\frac{9}{25}\)
\(=\frac{5}{11}+\frac{6}{11}+\frac{1}{14}+\frac{3}{4}+\frac{2}{5}+\frac{6}{25}+\frac{9}{25}\)
\(=1+\frac{23}{28}+1\)
\(=\frac{79}{28}\)
Bạn có thể xem ở đây : Tại đây
=1/14 +1/4+(2/5+6/25+9/25)+(6/11+5/11)
=4/64+16/64+1+1
=20/64+1+1
=5/16+1+1
=2 và 5/16
Cho mình sửa lại đề tí nhé bạn , nếu có gì sai liên hệ với mình !
\(\frac{5}{11}+\frac{1}{4}+\frac{2}{5}+\frac{6}{11}+\frac{3}{4}+\frac{6}{25}+\frac{9}{25}\)
\(=\frac{5}{11}+\frac{6}{11}+\frac{1}{4}+\frac{3}{4}+\frac{2}{5}+\frac{6}{25}+\frac{9}{25}\)
\(=1+1+1\)
\(=3\)
\(B=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{8.9.10.11}+\frac{1}{9.10.11.12}\)
\(B=\frac{1}{3}\left(\frac{3}{1.2.3.4}+\frac{3}{2.3.4.5}+\frac{3}{3.4.5.6}+...+\frac{3}{8.9.10.11}+\frac{3}{9.10.11.12}\right)\)
\(B=\frac{1}{3}\left(\frac{1}{1.2.3}-\frac{1}{2.3.4}+\frac{1}{2.3.4}-\frac{1}{3.4.5}+...+\frac{1}{9.10.11}-\frac{1}{10.11.12}\right)\)
\(B=\frac{1}{3}\left(\frac{1}{1.2.3}-\frac{1}{10.11.12}\right)\)
\(B=\frac{1}{3}.\frac{73}{440}=\frac{43}{1320}\)
viết rõ lại cái đề giùm tui tui mới làm được
\(\frac{6}{11}+\frac{1}{4}+\frac{5}{11}+\frac{3}{4}\)
\(=\left(\frac{6}{11}+\frac{5}{11}\right)+\left(\frac{1}{4}+\frac{3}{4}\right)\)
\(=\frac{11}{11}+\frac{4}{4}\)
\(=1+1\)
\(=2\)
\(\frac{6}{11}+\frac{1}{4}+\frac{5}{11}+\frac{3}{4}\)
\(=\left(\frac{6}{11}+\frac{5}{11}\right)+\left(\frac{1}{4}+\frac{3}{4}\right)\)
\(=1+1\)
\(=2\)