Đặt biểu thức trên là A
\(5A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{128}\)
Đặt \(B=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+..+\frac{1}{128}\)
\(2B=1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{64}\)
\(B=2B-B=1-\frac{1}{128}=\frac{127}{128}\)
\(5A=1+\frac{127}{128}=\frac{255}{128}\Rightarrow A=\frac{5A}{5}=\frac{51}{128}\)
Tính nhanh: \(\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+....+\frac{1}{1280}\)
Tính nhanh:
\(1\frac{1}{3}x2\frac{1}{4}x3\frac{1}{5}x4\frac{1}{6}x5\frac{1}{7}x6\frac{1}{8}x7\frac{1}{9}x8\frac{1}{10}\)
1,Tính nhanh
\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)
Tính nhanh : \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}\)
Hãy tính bằng cách hợp lí;\(\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+......+\frac{1}{1280}\)
Ai đúng mị tick cho
Tính nhanh:
A=\(\left(\frac{2}{5}+\frac{2}{9}+\frac{2}{11}\div\frac{7}{5}+\frac{7}{9}+\frac{7}{11}\right)\div\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{5}\div\frac{7}{6}-\frac{7}{8}+\frac{7}{10}\right)\)
Tính nhanh :
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}=\)
tính nhanh:
\(\frac{25.18+2,5.128+29,2.25}{1+5+9+.........+97+225}\)
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+........+\frac{1}{9900}\)
Tính nhanh:
\(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}\)
