Các câu hỏi tương tự
Tính \(B=\frac{1}{10\cdot9}+\frac{1}{18\cdot13}+\frac{1}{26\cdot17}+.............+\frac{1}{802\cdot405}\)
A=\(\frac{^{3^2}}{1\cdot4}\)+ \(\frac{3^2}{4\cdot7}\)+ \(\frac{3^2}{7\cdot10}\)+ \(\frac{3^2}{10\cdot13}\)+\(\frac{3^2}{13\cdot16}\)+......+ \(\frac{3^2}{97\cdot100}\)
Tinh nhanh:
\(\frac{7}{1\cdot5}+\frac{7}{5\cdot9}+\frac{7}{9\cdot13}+\frac{7}{13\cdot17}+\frac{7}{17\cdot21}\)
B=\(\frac{5}{1\cdot4}\)+\(\frac{5}{4\cdot7}\)+\(\frac{5}{7\cdot10}\)+\(\frac{5}{10\cdot13}\)+\(\frac{5}{13\cdot16}\)
\(x-\frac{20}{11\cdot13}-\frac{20}{13\cdot15}-\frac{20}{15\cdot17}-...-\frac{20}{53\cdot55}=\frac{3}{11}\)
\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+...+\frac{1}{x\left(x+1\right)}=\frac{2}{9}\)
Tìm x thuộc N
\(x-\frac{20}{11\cdot13}-\frac{20}{13\cdot15}-\frac{20}{15\cdot17}-...-\frac{20}{53\cdot55}=\frac{3}{11}\)
\(x+\frac{2}{35}+\frac{2}{63}+...+\frac{2}{399}=\frac{2}{7}\)
\(\frac{4}{1\cdot5}\)+\(\frac{4}{5\cdot9}\)+\(\frac{4}{9\cdot13}\)+\(\frac{4}{13\cdot17}\)+\(\frac{4}{17\cdot21}\)< 1
\(A=\frac{1}{1\cdot3}+\frac{2}{3\cdot7}+\frac{3}{7\cdot13}+...+\frac{10}{91\cdot111}\)
tính nhanh
\(\frac{6^2}{5\cdot7}\cdot\frac{7^2}{6\cdot8}\cdot\frac{8^2}{7\cdot9}\cdot\frac{9^2}{8\cdot10}\)