\(7.\left(\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+...+\frac{1}{69.70}\right)\\ 7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+....+\frac{1}{69}-\frac{1}{70}\right)\\ 7.\left(\frac{1}{10}-\frac{1}{70}\right)\\ 7.\frac{6}{70}=\frac{3}{5} \)
Tính nhanh
1)A=\(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
2)B=\(\frac{1}{25.27}+\frac{1}{27.29}+\frac{1}{29.31}+...+\frac{1}{73.75}\)
3)C=\(\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+...+\frac{4}{2008.2010}\)
\(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
\(B=\frac{1}{18}+\frac{1}{54}+\frac{1}{108}+...+\frac{1}{990}\)
\(C=\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
tính nhanh
\(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\) số cuối là số 69.70 nha
các bn giúp nha
Tính bằng cách hợp lí
a)\(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+....+\frac{7}{69.70}\)
b)\(\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
giúp mik với, mik đag cần gấp.Tks
cho a) A = \(\frac{1}{2}\)+ \(\frac{1}{3}\)+ \(\frac{1}{4}\)+....+\(\frac{1}{309}\), B = \(\frac{308}{1}\)+ \(\frac{307}{2}\)+....+ \(\frac{2}{307}\)+ \(\frac{1}{308}\). Tính \(\frac{A}{B}\)
b) \(\frac{7}{10.11}\)+ \(\frac{7}{11.12}\)+ \(\frac{7}{12.13}\)+....+ \(\frac{7}{69.70}\)
\(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
bài 1 : Tính
1) \(\left(\frac{1}{2}+1\right).\left(\frac{1}{3}+1\right).\left(\frac{1}{4}+1\right).....\left(\frac{1}{99}+1\right)\)
2) \(\left(\frac{1}{2}-1\right).\left(\frac{1}{3}-1\right).\left(\frac{1}{4}-1\right).....\left(\frac{1}{99}-1\right)\)
3) \(\frac{3}{2^2}.\frac{8}{3^2}.\frac{15}{4^2}...........\frac{899}{30^2}\)
4) \(\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+......+\frac{4}{107.111}\)
5) \(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+.........+\frac{2}{399}\)
6) \(\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+....+\frac{7}{69.70}\)
7) \(\frac{6}{15.18}+\frac{6}{18.21}+\frac{6}{21.24}+.....+\frac{6}{87.90}\)
\(a=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}.....+\frac{7}{69.70}\)
\(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)
