\(=\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{2.\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}+\frac{6}{7}\)

\(=\frac{1}{2}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{2}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}+\frac{6}{7}\)

\(=\frac{1}{2}.\frac{2}{7}+\frac{6}{7}\)

\(=1\)

\(\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{2\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}+\frac{6}{7}\)

\(=\frac{1}{2}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{7.\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}+\frac{6}{7}\)

\(=\frac{1}{2}.\frac{1}{\frac{7}{2}}+\frac{6}{7}=\frac{1}{2}.\frac{2}{7}+\frac{6}{7}=\frac{1}{7}+\frac{6}{7}=1\)

\(\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}\cdot\frac{\frac{1}{3}-0,25+0,2}{1\frac{1}{6}-0,875+0,7}\)

\(=\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{2.\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}\cdot\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}\)

\(=\frac{1}{2}\cdot\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{2}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}=\frac{1}{2}\cdot\frac{1}{\frac{7}{2}}=\frac{1}{2}\cdot\frac{2}{7}=\frac{1}{7}\)

ko biết viết chên này

\(A=\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}.\frac{\frac{1}{3}-0,25+0,2}{\frac{7}{6}-0,875+0,7}+\frac{6}{7}\)

\(=\frac{1}{2}.\frac{2}{7}+\frac{6}{7}=1\)

\(A=\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}.\frac{\frac{1}{3}-0,25+0,2}{\frac{7}{6}-0,875+0,7}+\frac{6}{7}\)

\(=\frac{1}{2}-\frac{1}{2}-\frac{1}{2}.\frac{5}{6}-\frac{25}{\frac{100}{-\frac{875}{1000}}}+\frac{6}{7}\)

\(=-\frac{1}{2}.\frac{5}{6}-\frac{25}{\frac{100}{\frac{-87,5}{100}}}+\frac{6}{7}\)

\(=-\frac{1}{2}.\frac{5}{6}-\frac{25}{-87,5}+\frac{6}{7}\)

đến đây tự lm == 

\(B=\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}\times\frac{\frac{1}{3}-0.25+0.2}{1\frac{1}{6}-0.875+0.7}+\frac{6}{7}\)\(\frac{6}{7}\)

\(B=\frac{1\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}{2\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}\times\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}+\frac{6}{7}\)

\(=\frac{1}{2}\times\frac{1\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}{7\left(\frac{1}{6}-\frac{1}{8}+\frac{1}{10}\right)}\times\frac{6}{7}\)

\(=\frac{1}{2}\times\frac{1\left(\frac{2}{6}-\frac{2}{8}+\frac{2}{10}\right)}{7\left(\frac{1}{6}-\frac{1}{8}+\frac{1}{10}\right)}\times\frac{6}{7}\)

\(=\frac{1}{2}\times\frac{1\times1}{7\times2}\times\frac{6}{7}=\frac{6}{2\times7\times2\times7}=\frac{3}{98}\)

xin lỗi mình làm sai một tí, bây giờ mình làm lại nha

Bài lm của Quang Nhat có đúng ko

\(\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{\dfrac{2}{3}-\dfrac{2}{7}-\dfrac{2}{13}}\cdot\dfrac{\dfrac{1}{3}-0,25+0,2}{1\dfrac{1}{6}-0,875+0,7}+\dfrac{6}{7}\)

\(=\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{2\cdot\left(\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}\right)}\cdot\dfrac{\dfrac{2}{6}-\dfrac{2}{8}+\dfrac{2}{10}}{\dfrac{7}{6}-\dfrac{7}{8}+\dfrac{7}{10}}+\dfrac{6}{7}\)

\(=\dfrac{1}{2}\cdot\dfrac{2\cdot\left(\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{10}\right)}{7\cdot\left(\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{10}\right)}+\dfrac{6}{7}\)

\(=\dfrac{1}{2}\cdot\dfrac{2}{7}+\dfrac{6}{7}\)

\(=\dfrac{1}{7}+\dfrac{6}{7}=\dfrac{7}{7}=1\)

\(\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{\dfrac{2}{3}-\dfrac{2}{7}-\dfrac{2}{13}}.\dfrac{\dfrac{1}{3}-0,25+0,2}{1\dfrac{1}{6}+0,875+0,7}+\dfrac{6}{7}.\)

\(=\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{2\left(\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}\right)}.\dfrac{\dfrac{2}{6}-\dfrac{2}{8}+\dfrac{2}{10}}{\dfrac{7}{6}-\dfrac{7}{8}+\dfrac{7}{10}}+\dfrac{6}{7}.\)

\(=\dfrac{1}{2}.\dfrac{2\left(\dfrac{1}{6}+\dfrac{1}{8}+\dfrac{1}{10}\right)}{7\left(\dfrac{1}{6}+\dfrac{1}{8}+\dfrac{1}{10}\right)}+\dfrac{6}{7}.\)

\(=\dfrac{1}{2}.\dfrac{2}{7}+\dfrac{6}{7}.\)

\(=\dfrac{1}{7}+\dfrac{6}{7}=\dfrac{7}{7}=1.\)

Vậy.....

\(\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}.\frac{\frac{1}{3}-0,25+0,2}{1\frac{1}{6}-0,875+0,7}+\frac{6}{7}\)

= \(\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{2\left(\frac{1}{3}-\frac{1}{7}-\frac{1}{13}\right)}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{\frac{7}{6}-\frac{7}{8}+\frac{7}{10}}+\frac{6}{7}\)

= \(\frac{1}{2}.\frac{\frac{1}{3}-\frac{1}{4}+\frac{1}{5}}{7.\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\right)}+\frac{6}{7}\)

= \(\frac{1}{2}.\frac{1}{\frac{7}{2}}+\frac{6}{7}\)

= \(\frac{1}{2}.\frac{2}{7}+\frac{6}{7}\)

= \(\frac{1}{7}+\frac{6}{7}\)

= 1

\(=\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{2\left(\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}\right)}.\dfrac{\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}}{\dfrac{7}{6}-\dfrac{7}{8}+\dfrac{7}{10}}+\dfrac{6}{7}\)

\(=\dfrac{1}{2}.\dfrac{\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}}{\dfrac{7}{2}\left(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}\right)}+\dfrac{6}{7}\)

\(=\dfrac{1}{2}.\dfrac{2}{7}+\dfrac{6}{7}=\dfrac{1}{7}+\dfrac{6}{7}=1\)