Question

\(\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+.........+\frac{1}{1280}?\)    

lời giải chi tiết nha , mình đang cần gấp 

Answer 1

A = 1/5 + 1/10 + 1/20 + 1/40 + ..... + 1/1280

A x 2 = 2/5 - ( 1 /5 + 1/10 + 1/20 + 1/40 + ... + 1/1280 ) - 1/1280

A x 2 = 2/5 - A - 1/1280

A x 2 - A = 2/5 - 1/1280

A  = 2/5 - 1/1280

A = 511/1280

Answer 2

A = 1/5 + 1/10 + 1/20 + 1/40 + ..... + 1/1280

A x 2 = 2/5 - ( 1 /5 + 1/10 + 1/20 + 1/40 + ... + 1/1280 ) - 1/1280

A x 2 = 2/5 - A - 1/1280

A x 2 - A = 2/5 - 1/1280

A  = 2/5 - 1/1280

A = 511/1280

Answer 3

\(=\frac{1}{5}+\frac{1}{5}\cdot\frac{1}{2}+\frac{1}{5}\cdot\frac{1}{2^2}+\frac{1}{5}\cdot\frac{1}{2^3}+...+\frac{1}{5}\cdot\frac{1}{2^8}\)

\(=\frac{1}{5}\cdot\left(1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^8}\right)=\frac{1}{5}\cdot2\cdot\left(1-\frac{1}{2}\right)\cdot\left(1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^8}\right)\)

\(=\frac{2}{5}\cdot\left(1-\frac{1}{2^9}\right)=\frac{2\cdot\left(2^9-1\right)}{5\cdot2^9}=\frac{511}{1280}\)

Answer 4

\(\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+....+\frac{1}{1280}\)

\(\left(\frac{2}{5}-\frac{1}{5}\right)+\left(\frac{1}{5}-\frac{1}{10}\right)+....+\left(\frac{1}{640}-\frac{1}{1280}\right)\)

TA TRIỆT TIÊU PHÉP TÍNH CHỈ CÒN LẠI \(\frac{2}{5}\)VÀ \(\frac{1}{1280}\)(VÌ NẾU \(-\frac{1}{5}\)RỒI LẠI \(+\frac{1}{5}\)THÌ =0 TƯƠNG TỰ NHƯ VẬY TA CHỈ CÒN \(\frac{2}{5}\)VÀ \(\frac{1}{1280}\)

TA CÓ :\(\frac{2}{5}-\frac{1}{1280}=\frac{511}{1280}\)

Answer 5

đéo biết

Answer 6

1/20+2/4+3/100 bằng bao nhiêu vậy