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\(\left(1-\frac{1}{21}\right).\left(1-\frac{1}{28}\right).\left(1-\frac{1}{36}\right)...\left(1-\frac{1}{1326}\right)\)
\(=\frac{20}{21}.\frac{27}{28}.\frac{35}{36}...\frac{1325}{1326}\)
\(=\frac{40}{42}.\frac{54}{56}.\frac{70}{72}...\frac{2650}{2652}\)
\(=\frac{5.8}{6.7}.\frac{6.9}{7.8}.\frac{7.10}{8.9}...\frac{50.53}{51.52}\)
\(=\frac{5.6.7...50}{7.8.9...52}.\frac{8.9.10...53}{6.7.8...51}\)
\(=\frac{5.6}{51.52}.\frac{52.53}{6.7}\)
\(=\frac{5.52}{51.7}=\frac{260}{357}\)
Ủng hộ mk nha ^_-
\(A=\frac{14}{15}.\frac{20}{21}.\frac{27}{28}....\frac{209}{210}=\frac{28}{30}.\frac{40}{42}.\frac{54}{56}....\frac{418}{420}=\frac{4.7}{5.6}.\frac{5.8}{6.7}.\frac{6.9}{7.8}....\frac{19.22}{20.21}\)
\(=\frac{4.5.6...19}{5.6.7...20}.\frac{7.8.9...22}{6.7.8...21}=\frac{4}{20}.\frac{22}{6}=\frac{11}{5}\)
\(\Rightarrow A=\frac{14}{15}.\frac{20}{21}.\frac{41}{42}.....\frac{209}{210}\)
\(=\frac{4.7}{5.6}.\frac{5.8}{6.7}.\frac{6.9}{7.8}.....\frac{19.22}{20.21}\)
\(=\frac{22}{6}=\frac{11}{3}\)
\(\left(\frac{-1}{4}+\frac{7}{33}-\frac{5}{3}\right)-\left(\frac{-5}{4}+\frac{6}{11}-\frac{48}{49}\right)=\left(\frac{-1}{4}-\frac{16}{11}\right)-\left(-\frac{31}{44}-\frac{48}{49}\right)=-\frac{1}{4}-\frac{16}{11}+\frac{31}{44}+\frac{48}{49}=-\frac{1}{49}\)
(1-1/15).(1-1/21).(1-1/28)...(1-1/210)
xin loi nhung ma minh cung dang khong giai duoc cau nay, minh mong cac ban tren Online Math giup minh nhe