5/34

TICK CHO MIK NHA!

ai tk cho cả

Ta có : \(\frac{1}{10}+\frac{1}{40}+\frac{1}{88}+\frac{1}{154}+\frac{1}{238}+\frac{1}{340}\)

\(=\frac{1}{2\times5}+\frac{1}{5\times8}+\frac{1}{8\times11}+\frac{1}{11\times14}+\frac{1}{14\times17}+\frac{1}{17\times20}\)

\(=\frac{1}{3}\times\left(\frac{3}{2\times5}+\frac{3}{5\times8}+\frac{3}{8\times11}+\frac{3}{11\times14}+\frac{3}{14\times17}+\frac{3}{17\times20}\right)\)

\(=\frac{1}{3}\times\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+\frac{1}{17}-\frac{1}{20}\right)\)

\(=\frac{1}{3}\times\left(\frac{1}{2}-\frac{1}{20}\right)\)

\(=\frac{1}{3}\times\frac{9}{20}\)

\(=\frac{3}{20}\)

Đặt \(A=\frac{1}{10}+\frac{1}{40}+\frac{1}{88}+\frac{1}{154}+\frac{1}{238}+\frac{1}{340}\) 

=> \(A=\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+\frac{1}{11.14}+\frac{1}{14.17}+\frac{1}{17.20}\)    (dấu . có nghĩa là nhân)

=> \(3A=3\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+\frac{1}{11.14}+\frac{1}{14.17}+\frac{1}{17.20}\right)\)

\(=\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}+\frac{3}{14.17}+\frac{3}{17.20}\)

\(=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+\frac{1}{17}-\frac{1}{20}\)

\(=\frac{1}{2}-\frac{1}{20}\) 

\(=\frac{9}{20}\)            

Đây là kiến thức lớp 6 nhá =)) bạn mà có chỗ nào ko hiểu thì hỏi ng thầy cô giạy bạn ý

\(\frac{1}{10}+\frac{1}{40}+\frac{1}{88}+\frac{1}{154}+\frac{1}{238}+\frac{1}{340}\)

\(=\frac{1}{2\cdot5}+\frac{1}{5\cdot8}+\frac{1}{8\cdot11}+\frac{1}{11\cdot14}+\frac{1}{14\cdot17}+\frac{1}{17\cdot20}\)

\(=\frac{1}{3}\left(\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+\frac{3}{11\cdot14}+\frac{3}{14\cdot17}+\frac{3}{17\cdot20}\right)\)

\(=\frac{1}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{17}-\frac{1}{20}\right)\)

\(=\frac{1}{3}\left(\frac{1}{2}-\frac{1}{20}\right)\)

\(=\frac{1}{3}\cdot\frac{9}{20}\)

\(=\frac{3}{20}\)

A =  1/10 + 1/40 + 1/88 + 1/154 + 1/238 + 1/340 

A = 1/2.5 + 1/5.8 + 1/8.11 + 1/11.14 + 1/14.17 + 1/17.20

3 A = 3/2.5 + 3/5.8 + 3/8.11 + ... + 3/17.20

3A = 1/2 - 1/5 + 1/5 - 1/8 + ... + 1/17 - 1/20

3A = 1/2 - 1/20

3A = 9/20

A = 9/20 : 2

1/10+1/40+1/88+1/154+1/238+1/340

=1/2.5+1/5.8+1/8.11+1/11.14+1/14.17+1/17.20

=1/2-1/5+1/5-1/8+1/8-...+1/17-1/20

=1/2-1/20

=9/20

​k cho mình nha thanks bạn

= 3/30 nhé bạn

\(\frac{3}{20}\)

k mk nhé 

bạn có thể trả lời đầy đủ ko

8,112

Ta có A = 1/2×5 -1/5×8 -1/8×11 -1/11×14 -1/14×17 -1/17*20

=>A3= 3/2×5 -3/5×8 -3/8×11 -3/11×14 -3/14×17 -3/17×20

=>A3= 1/2 -1/5 -1/5 +1/8 -1/8 +1/11 -1/11+1/14 -1/14 +1/17 -1/17 +1/20

=>A3= 1/2 -1/5-1/5+1/20

=>A3= 10/20 -4/20 -4/20 +1/20= 3/20

=>A=3/20:3

=> A =1/20 

Có j ko hiu hỏi mk nha

giúp mk bài dưới dc k

Mk lm câu b trc nha

3 mũ x+1 . 5 mũ y = 3 mũ 2x . 5 mũ x

=> 3 mũ x+1= 3 mũ 2x và 5 mũ y = 5 mũ x

=> x+1=2x và x=y

Từ x+1 =2x => 2x-x=1 => x=1 

Mà x= y=>x=y=1

Vậy..