Ta có:2A=\(2+1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\)

2A-A=\(\left(2+1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\right)-\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\right)\)

\(=2-\frac{1}{32}=\frac{63}{32}=A\)

Ta có: \(A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\)

\(\Rightarrow A=1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+\frac{1}{2^5}\)

\(\Rightarrow2A=2+1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}\)

\(\Rightarrow2A-A=\left(2+1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}\right)-\left(1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+\frac{1}{2^5}\right)\)

\(\Rightarrow A=1-\frac{1}{2^5}=\frac{31}{32}\)

Vậy \(A=\frac{31}{32}\)

1/2=1- 1/2

1/4=1/2 -1/4

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

A=1+1-1/36

71/36

d

D

1 I will be helped by Adam

2 I will be helped with money by him

3 A new phone will be bought by Jenny

4 THe toy will be broken by the baby

5 Will the food be cooked by him

6 The watch won't be stolen by him

7 Why will the bill be paid by him?

8 What will be had for breakfast by you?

9 Her cloth won't be ironed by her

10 THe letter won't be posted by Jack

11 Why will these papers be signed by her?

12 The train will be caught by us

2-3+4-5.......+2008-2009+2010-2011

\(=\left(2-3\right)+\left(4-5\right)+......+\left(2008-2009\right)+\left(2010-2011\right)\)(có tất cả 1005 số hạng -1)

\(=-1.1005=-1005\)

Học tốt

bạn chưa giải thích rõ ràng

                Trồng cây theo hình ngôi sao nhé

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*            *            *            *

          *                    *        

                     *        

    *                                * 

Các bạn làm nhanh nhé  9 giờ mình phải nộp bài 😭😭😭😭mà không có ai giúp mình. 

Làm giúp mình với nhé!😭😭😭😭😭

Gấp lắm nha

1 C
2 A
3 B
4 C

1. C              2. A
3. B              4 C

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