393984 nhé !

393984

tk

\(A=\dfrac{1}{3}\left(1+\dfrac{1}{2}+...+\dfrac{1}{256}+\dfrac{1}{512}\right)\)

Đặt B=1+1/2+...+1/256+1/512

=>2B=2+1+...+1/128+1/256

=>B=2-1/512=1023/512

=>\(A=\dfrac{1}{3}\cdot\dfrac{1023}{512}=\dfrac{341}{512}\)

X*3069=3069

X=3069/3069

X-1

X = 3069/3069

X = 1

k cho minh nha

A = 3 + 6 + 12 +24 + ... + 768 + 1536

A x 2 = 6 + 12 + 24 + 48 + ... + 1536 + 3072

A = 3 + 3072 = 3075

chịu nha bạn

A = 3 + 6 + 12 + 24 + ... + 768 + 1536

A x 2 = 6 + 12 + 24 + 48 + ... + 1536 + 3072

A = 3072 - 3  = 3069

\(A=\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}+\frac{1}{384}+\frac{1}{768}+\frac{1}{1536}\)

\(A\times2=\frac{2}{3}+\frac{2}{6}+\frac{2}{12}+\frac{2}{24}+\frac{2}{48}+\frac{2}{96}+\frac{2}{192}+\frac{2}{384}+\frac{2}{768}+\frac{2}{1536}\)

Rút gọn ta được

\(A\times2=\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}+\frac{1}{384}+\frac{1}{768}\)

\(A\times2-A=\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{768}-\left[\frac{1}{3}+\frac{1}{6}+...+\frac{1}{1536}\right]\)

\(A=\frac{2}{3}+\frac{1}{3}-\frac{1}{3}-\frac{1}{1536}\)

\(A=\frac{2}{3}-\frac{1}{1536}=\frac{341}{512}\)

Bạn hiểu cách làm lớp 6 ko mk gửi

Đáp số: 341/512

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+...+\frac{1}{1536}+\frac{1}{3072}\)

\(=\frac{2}{3}-\frac{1}{3}+\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{12}+\frac{1}{12}-\frac{1}{24}+...+\frac{1}{1536}-\frac{1}{3072}\)

\(=\frac{2}{3}+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{6}-\frac{1}{6}\right)+\left(\frac{1}{12}-\frac{1}{12}\right)+...+\left(\frac{1}{1536}-\frac{1}{1536}\right)-\frac{1}{3072}\)

\(=\frac{2}{3}-\frac{1}{3072}\)

\(=\frac{2047}{3072}\)

 Mình cũng ra đáp số 2047/3072