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26 tháng 6 2021

\(A=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}}{2020+\frac{2019}{2}+...+\frac{1}{2020}}\)

\(=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}}{1+\left(\frac{2019}{2}+1\right)+\left(\frac{2018}{3}+1\right)...+\left(\frac{1}{2020}+1\right)}\)

\(=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}}{\frac{2021}{2021}+\frac{2021}{2}+\frac{2021}{3}+...+\frac{2021}{2020}}\)
\(=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}}{2021\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}\right)}=\frac{1}{2021}\)

Vậy \(A=\frac{1}{2021}\).

27 tháng 11 2021

1 were - would you play

2 weren't studying - would have 

3 had taken - wouldn't have got

4 would you go - could

5 will you give - is

6 recycle - won't be

7 had heard - wouldn't have gone

8 would you buy - had

9 don't hurry - will miss

10 had phoned - would have given

11 were - wouldn't eat

12 will go - rains

13 had known - would have sent

14 won't feel - swims

15 hadn't freezed - would have gone

1 tháng 12 2021

Bài mấy?

1 tháng 12 2021

bài 1,2,3,4,5,6 

là tất cả

 

8 tháng 11 2021

bài đâu bn?

27 tháng 11 2021

1 had stayed

2 were

3 arrive

4 would have bought

5 would go

6 comes

7 had thought

8 gets

9 will become

10 had known

11 hurries

12 would change

13 would have trusted 

14 doesn't study

15 weren't