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

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

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

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

20 : x + 30 : x = 50

   (20 + 30) : x = 50

              50 : x = 50

                     x = 50 : 50

                    x = 1

Vậy x = 1

20 : x + 30 : x = 50

( 20 + 30 )  : x  = 50

50             :  x  = 50

                    x = 50 : 50

                    x = 1

(20+30):x=50

50:x=50

 x=50:50

x=1

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)

\(=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}\)

\(=\frac{2-1}{1\cdot2}+\frac{3-2}{2\cdot3}+...+\frac{6-7}{6\cdot7}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{6}-\frac{1}{7}\)

\(=1-\frac{1}{7}\)

\(=\frac{6}{7}\)

=6/7

nhớ tk cho tui nha ^_^

tk đi tk lại cho

6/7 nha bn

k cho mik nha yêu bn nhiều

1-2+3-4+5-6+......+101-102+103

\(\left(1-2\right)+\left(3-4\right)+\left(5-6\right)+...+\left(101-102\right)+103\)

\(\left(-1\right)+\left(-1\right)+\left(-1\right)+...+\left(-1\right)+103\)( có 51 cặp số (1) )

\(\left(-51\right)+103\)

\(52\)

Vậy ...

1-2+3-4+5-6+......+101-102+103

=(103 - 102)+(101 - 100)+...+(7 - 6)+(5 - 4)+(3 - 2)+1

Ta thấy dãy trên có 51 cặp , mỗi cặp đều có tổng bằng 1.

= 1 * 51 +1

=1 * 52

=52.

52 nha

k nha