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Để mình làm lại nguyên bài cho dễ hiểu nhé
\(A=\frac{2}{60.63}+\frac{2}{63.66}+\frac{2}{66.69}+..+\frac{2}{117.120}+\frac{2}{2011}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{63}+\frac{2}{63}-\frac{2}{66}+\frac{2}{66}-\frac{2}{69}+...+\frac{2}{117}-\frac{2}{120}\right)+\frac{2}{2011}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{120}\right)+\frac{2}{2011}=\frac{2}{3}.\frac{1}{60}+\frac{2}{2011}=\frac{4382}{361980}\)
Sorry nhé! nãy giờ nhìn không kĩ đề
\(A=\frac{2}{60.63}+\frac{2}{63.66}+\frac{2}{66.69}+...+\frac{2}{117.120}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{63}+\frac{2}{63}-\frac{2}{66}+\frac{2}{66}-\frac{2}{69}+...+\frac{2}{117}-\frac{2}{120}\right)\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{120}\right)=\frac{2}{3}.\frac{1}{60}=\frac{2}{180}\)
Suy ra \(A=\frac{2}{180}\)
a)\(\frac{2}{3}+\frac{3}{4}+\frac{5}{6}\)
\(=\frac{8+9+10}{12}\)
\(=\frac{27}{12}=\frac{9}{4}\)
b)\(\frac{15}{8}-\frac{7}{12}+\frac{5}{6}\)
\(=\frac{45-14+20}{24}\)
\(=\frac{51}{24}=\frac{17}{8}\)
2)
a)\(\frac{2}{5}+\frac{7}{13}+\frac{3}{5}+\frac{1}{7}\)
\(=\frac{2}{5}+\frac{3}{5}+\frac{7}{13}+\frac{1}{7}\)
\(=1+\frac{7}{13}+\frac{1}{7}\)
\(=\frac{20}{13}+\frac{1}{7}\)
\(=\frac{153}{91}\)
Tí tớ trả lời tiếp
c.
\(\frac{1}{3}\times\frac{5}{7}-\frac{7}{27}\times\frac{36}{14}\)
\(=\frac{1}{3}\times\frac{5}{7}-\frac{7}{3\times9}\times\frac{4\times9}{7\times2}\)
\(=\frac{1}{3}\times\frac{5}{7}-\frac{1}{3}\times\frac{4}{6}\)
\(=\frac{1}{3}\times\left(\frac{5}{7}-\frac{4}{6}\right)\)
\(=\frac{1}{3}\times\left(\frac{30-38}{42}\right)\)
\(=\frac{1}{3}\times\frac{-8}{42}\)
\(=-\frac{4}{63}\)
Chúc bạn học tốt
\(a,\frac{1}{1-\frac{1}{1-\frac{1}{2}}}+\frac{1}{1+\frac{1}{1+\frac{1}{2}}}\)
\(=\frac{1}{1-\frac{1}{\frac{1}{2}}}+\frac{1}{1+\frac{1}{\frac{3}{2}}}\)
\(=\frac{1}{1-2}+\frac{1}{1+\frac{2}{3}}\)
\(=\frac{1}{-1}+\frac{1}{\frac{5}{3}}\)
\(=-1+\frac{3}{5}=-\frac{2}{5}\)
\(b,\frac{1}{1-\frac{1}{1-\frac{1}{3}}}+\frac{1}{1+\frac{1}{1+\frac{1}{3}}}\)
\(=\frac{1}{1-\frac{1}{\frac{2}{3}}}+\frac{1}{1+\frac{1}{\frac{4}{3}}}\)
\(=\frac{1}{1-\frac{3}{2}}+\frac{1}{1+\frac{3}{4}}\)
\(=\frac{1}{-\frac{1}{2}}+\frac{1}{\frac{7}{4}}\)
\(=-2+\frac{4}{7}=-\frac{10}{7}\)