tính nhanh 

49/5-1/2-1/4-1/8-1/16-1/32=8,83125

nha bn duyệt đi

\(\frac{49}{5}-\frac{1}{2}-\frac{1}{4}-\frac{1}{8}-\frac{1}{16}-\frac{1}{32}=\frac{1413}{160}=8,83125\)

Nhanh lên giúp tớ

1413/160

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

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

\(A=\dfrac{49}{5}-\left(1-\dfrac{1}{32}\right)=\text{​​}\dfrac{49}{5}-\dfrac{31}{32}\text{​​}\)

\(A=\dfrac{1413}{160}\text{​​}\)

b: A=1/3+1/9+...+1/3^10

=>3A=1+1/3+...+1/3^9

=>A*2=1-1/3^10=(3^10-1)/3^10

=>A=(3^10-1)/(2*3^10)

c: C=3/2+3/8+3/32+3/128+3/512

=>4C=6+3/2+...+3/128

=>3C=6-3/512

=>C=1023/512

d: A=1/2+...+1/256

=>2A=1+1/2+...+1/128

=>A=1-1/256=255/256

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

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

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

a. \(\dfrac{17}{13}-\dfrac{14}{23}+\dfrac{9}{13}-\dfrac{9}{23}=\left(\dfrac{17}{13}+\dfrac{9}{13}\right)-\left(\dfrac{14}{23}+\dfrac{9}{23}\right)=\dfrac{26}{13}-\dfrac{23}{23}=2-1=1\)

b.\(\dfrac{49}{5}-\dfrac{1}{2}-\dfrac{1}{4}-\dfrac{1}{32}-\dfrac{1}{16}-\dfrac{1}{32}=\dfrac{49}{5}-\left(1-\dfrac{1}{32}\right)=\dfrac{44}{5}+\dfrac{1}{32}=\dfrac{1413}{160}\)

= \(\dfrac{49}{2}-\dfrac{1}{2}-\dfrac{1}{4}-\dfrac{1}{8}-\dfrac{1}{16}-\dfrac{1}{32}\)

= \(\dfrac{784}{32}-\dfrac{16}{32}-\dfrac{8}{32}-\dfrac{4}{32}-\dfrac{2}{32}-\dfrac{1}{32}\)

= \(\dfrac{753}{32}\)

       A =       \(\dfrac{49}{2}\) - \(\dfrac{1}{2}\) - \(\dfrac{1}{4}\) - \(\dfrac{1}{8}\) - \(\dfrac{1}{16}\) - \(\dfrac{1}{32}\)

A \(\times\) 2  = 49 - 1 - \(\dfrac{1}{2}\)  - \(\dfrac{1}{4}\) - \(\dfrac{1}{8}\) - \(\dfrac{1}{16}\)

A \(\times\) 2  - A = 48 - \(\dfrac{49}{2}\) + \(\dfrac{1}{32}\)

            A  =   \(\dfrac{1536}{32}\) - \(\dfrac{784}{32}\) + \(\dfrac{1}{32}\)

             A = \(\dfrac{753}{32}\)

\(\dfrac{63}{64}\)

\(\dfrac{32}{64}+\dfrac{16}{64}+\dfrac{8}{64}+\dfrac{4}{64}+\dfrac{2}{64}+\dfrac{1}{64}=\dfrac{32+16+8+4+2+1}{64}=\dfrac{63}{64}\)

 1/2    + 1/4     + 1/8  + 1/16  + 1/32 + 1/64

 = 32/64 + 16/64 + 8/64 + 4/64 + 2/64 + 1/64

 =                         63/64