Ai trả lời câu hs giúp vs ạ

i don't care :))

9/4.7/17+2

=63/68+2

=63/68+136/68=199/68

1/4.3/1-21/4.13/17

=1/4.3/17-21/4.14/17

=3/68-273/68=-270/68=-135/68

Answer:

\(\dfrac{1}{2}+\dfrac{2}{4}+\dfrac{3}{8}+...+\dfrac{10}{2^{10}}\)

\(=\left(\dfrac{2}{2^0}-\dfrac{3}{2^1}\right)+\left(\dfrac{3}{2^1}-\dfrac{4}{2^2}\right)+\left(\dfrac{4}{2^2}+\dfrac{5}{2^3}\right)+...+\left(\dfrac{11}{2^9}-\dfrac{12}{2^{10}}\right)\)

\(=2-\dfrac{12}{2^{10}}\)

\(=2-\dfrac{3}{256}\)

\(=\dfrac{512}{256}-\dfrac{3}{256}\)

\(=\dfrac{509}{256}\)

*Để làm bài này dễ hơn, bạn áp dụng công thức sau:

\(\dfrac{n}{2^n}=\dfrac{n+1}{2^{n-1}}-\dfrac{n+2}{2^n}\)

=> 2x-4+6-x=8

=> 2x-x=8+4-6

=>x=6

2.(x-2)-3.(-2+x)=8

2.(x-2)-3.(x-2)=8

(x-2).(2-3)=8

(x-2).(-1)=8

x-2=8/(-1)= -8

x= -8+2= -6

Bài 2: 

a: =>2/3-x=-1/3

hay x=1

b: =>x=-2/5-2/5=-4/5

a: =>2/3-x=-1/3

hay x=1

b: =>x=-2/5-2/5=-4/5

D

C

=3/7*7/3*-2/5*20*19/72

=-8*19/72

=-19/9

a) Số học sinh giỏi là: 40:2=20(hs)
Số học sinh khá là: (40-20):5x3=12(hs)
Số học sinh trung bình là: 40-20-12=8(hs)
b) Tỉ số phần trăm số học sinh trung bình với số học sinh cả lớp là: 8:40x100%=20%
Đáp số:. ...

\(A=\dfrac{1}{2}+\dfrac{2}{4}+\dfrac{3}{8}+...+\dfrac{10}{2^{10}}\)

\(2A=\dfrac{1}{1}+\dfrac{2}{2}+\dfrac{3}{4}+...+\dfrac{10}{2^9}\)

\(2A-A=\left(1+\dfrac{2}{2}+\dfrac{3}{4}+...+\dfrac{10}{2^9}\right)-\left(\dfrac{1}{2}+\dfrac{2}{4}+...+\dfrac{10}{2^{10}}\right)\)

\(A=1+\dfrac{1}{2}+\dfrac{1}{4}+...+\dfrac{1}{2^9}-\dfrac{10}{2^{10}}\)

\(B=1+\dfrac{1}{2}+\dfrac{1}{4}+...+\dfrac{1}{2^9}\)

\(2B=2+1+\dfrac{1}{2}+...+\dfrac{1}{2^8}\)

\(2B-B=\left(2+1+\dfrac{1}{2}+...+\dfrac{1}{2^8}\right)-\left(1+\dfrac{1}{2}+\dfrac{1}{4}+...+\dfrac{1}{2^9}\right)\)

\(B=2-\dfrac{1}{2^9}\)

Suy ra \(A=B-\dfrac{10}{2^{10}}=2-\dfrac{1}{2^9}-\dfrac{10}{2^{10}}=\dfrac{509}{256}\)