b) 1/3+1/3^2+1/3^3+1/3^4+1/3^5 (goi tong bang M)

3M=1+1/3+1/3^2+1/3^3+1/3^4

3M-M=1-1/3^5

2M=242/243

M=242/243*1/2=121/243

^ là gì vậy 

mình gọi phép tính trên là Acho đỡ rối nha

có A=1-1/2+1/2-1/4+1/4-1/8+1/8-1/16+1/16-1/32

A=1-1/32

A=31/32

Ta có:

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

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

=31/32

\(\frac{1023}{1024}\)

1/3-1/4 + 1/4-1/5 + 1/5-1/6 + 1/6-1/7 +...+ 1/11-1/12= 1/3-1/12 =1/4

\(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{11\cdot12}\)

\(=\left(\frac{1}{3}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{5}\right)+\left(\frac{1}{5}-\frac{1}{6}\right)+...+\left(\frac{1}{11}-\frac{1}{12}\right)\)

\(=\frac{1}{3}-\frac{1}{12}=\frac{1}{4}\)

\(x+\frac{1}{2}+x+\frac{1}{4}+x+\frac{1}{8}+x+\frac{1}{16}=\frac{23}{16}=>4x=\frac{23}{16}-\frac{15}{16}=\frac{1}{2}=>x=\frac{1}{8}\)

(xx4)+1/2+1/4+1/8+1/16=23/16

xx4=23/16-(1/2+1/4+1/8+1/16)

xx4=1/2

x=1/2:4

x=1/8

Đúng 100% nhé Nhớ k cho mình đấy

1/2,1/3,1/4,1/6

\(=\frac{6}{12}+\frac{4}{12}+\frac{3}{12}+\frac{2}{12}+\frac{1}{12}\)

\(=\frac{27}{12}=\frac{9}{4}\)

Đáp án lần lượt là: \(\frac{23}{36};\frac{31}{7};\frac{1}{6};\frac{3}{5}\)

#Hk_tốt

#Ken'z

NGọc Ken nhanh nhất

=\(\frac{9}{3}\)=3 ai k mk mk k lại 3 k

Tổng trên bằng:

4/3+5/3=9/3=3

Đáp số:3

Trl 

56/76+65/76=121/76

Hok tốt 

Trl 

31/40+13/40=44/40=11/10

Hok tốt