\(\dfrac{7}{110}+\dfrac{7}{132}+\dfrac{7}{156}+...+\dfrac{7}{4830}\)
\(=\dfrac{7}{10\cdot11}+\dfrac{7}{11\cdot12}+\dfrac{7}{12\cdot13}+...+\dfrac{7}{69\cdot70}\)
\(=7\left(\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{13}+...+\dfrac{1}{69}-\dfrac{1}{70}\right)\)
\(=7\left(\dfrac{1}{10}-\dfrac{1}{70}\right)\)
\(=7\cdot\dfrac{3}{35}=\dfrac{3}{5}\)
giúp em với ạ. em cần gấp. camon
Tính bằng cách hợp lí:
a, 2 - (\(\dfrac{3}{7}\)+\(\dfrac{1}{3}\)) - (2- \(\dfrac{4}{3}\)+\(\dfrac{2}{7}\)) + 2 - (4-\(\dfrac{5}{7}\))
b, \(\dfrac{-3}{13}\) . (\(\dfrac{44}{33}\)+\(\dfrac{4444}{3030}\)+\(\dfrac{444444}{404040}\))
\(\left|\dfrac{1}{2}+\dfrac{-2}{3}\right|\dfrac{24}{7}-\dfrac{4}{7}.\dfrac{3}{5}+\dfrac{2}{5}.\left(\dfrac{-4}{7}\right)\)
Chỉ e vs ạ
Thực hiện phép tính:
a) \(\left(\dfrac{-3}{7}+\dfrac{4}{11}\right):\dfrac{7}{11}+\left(\dfrac{-4}{7}+\dfrac{7}{11}\right):\dfrac{7}{11}\)
b)\(\dfrac{1}{99.97}-\dfrac{1}{97.95}-\dfrac{1}{95.93}-...-\dfrac{1}{5.3}-\dfrac{1}{3.1}\)
Tính bằng cách thuận tiện nhất
B=\(\dfrac{1+\dfrac{1}{7}+\dfrac{1}{7^2}-\dfrac{1}{7^3}}{4+\dfrac{4}{7}+\dfrac{4}{7^2}-\dfrac{4}{7^3}}x\dfrac{858585}{313131}x\left(-1\dfrac{14}{17}\right)\)
Tính (hợp lí nếu có thể)
\(\dfrac{1}{3}\) - \(\dfrac{3}{5}\) + \(\dfrac{5}{7}\) - \(\dfrac{7}{9}\) + \(\dfrac{9}{11}\) - \(\dfrac{11}{13}\) + \(\dfrac{13}{15}\) + \(\dfrac{11}{13}\) - \(\dfrac{9}{11}\) + \(\dfrac{7}{9}\) - \(\dfrac{5}{7}\) + \(\dfrac{3}{5}\) - \(\dfrac{1}{3}\)
Tính nhanh:
\(a,A=\dfrac{\dfrac{5}{4}+\dfrac{5}{5}+\dfrac{5}{7}-\dfrac{5}{11}}{\dfrac{10}{4}+\dfrac{10}{5}+\dfrac{10}{7}-\dfrac{10}{11}}\)\(b,B=\dfrac{2+\dfrac{6}{5}-\dfrac{6}{7}-\dfrac{6}{11}}{\dfrac{2}{3}+\dfrac{2}{5}-\dfrac{2}{7}-\dfrac{2}{11}}\)
giúp mình với
\(40\dfrac{1}{4}:\dfrac{5}{7}-25\dfrac{1}{4}:\dfrac{5}{7}-\dfrac{1}{2021}\)
Mình đang cần gấp
Tính tổng:s=\(\left(-\dfrac{1}{7}\right)^0+\left(-\dfrac{1}{7}\right)^1+\left(-\dfrac{1}{7}\right)^2+...+\left(-\dfrac{1}{7}\right)^{2007}\)
Thực hiện phép tính (hợp lí nếu có thể):
a) \(13\dfrac{2}{7}\) : (\(\dfrac{-8}{9}\)) + \(2\dfrac{5}{7}\) : (\(\dfrac{-8}{9}\))
b) (\(\dfrac{-6}{11}\)) . \(\dfrac{7}{10}\) . (\(\dfrac{11}{-6}\)) . (-20)
c) (\(-1\dfrac{1}{2}\)) : \(\dfrac{3}{4}\) . (\(-4\dfrac{1}{2}\))
