Question

tính bằng cách thuận tiện nhất 

49/5 - 1/2 - 1/4 -1/8 - 1/16 - 1/32

 

Answer 1

Ta có : \(\frac{49}{5}-\frac{1}{2}-\frac{1}{4}-\frac{1}{8}-\frac{1}{16}-\frac{1}{32}\)

\(=\frac{49}{5}-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\right)\)

Đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\)

=> \(2A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\)

=> \(2A-A=1-\frac{1}{32}\Rightarrow A=\frac{31}{32}\)

Vậy \(\frac{49}{5}-\frac{1}{2}-\frac{1}{4}-\frac{1}{8}-\frac{1}{16}-\frac{1}{32}\)

\(=\frac{49}{5}-\frac{31}{32}=\frac{1413}{160}\)

Answer 2

\(\frac{49}{5}-\frac{1}{2}-\frac{1}{4}-\frac{1}{8}-\frac{1}{16}-\frac{1}{32}\)\(=\)\(\frac{4189}{480}\)