1/ 2 + 2 = 4

2/ 4 + 4 = 8

3/ 8 + 8 = 16

4/ 16 + 16 = 32

5/ 32 + 32 =64

6/ 64 + 64 =128

7/ 128 + 128 =256

8/  256 + 256 =512

9/ 521 + 512 =1033

10/ 2048 + 2048 =4096

k mình đi

4

8

16

32

64

128

256

512

2048

4096

b: A=1/3+1/9+...+1/3^10

=>3A=1+1/3+...+1/3^9

=>A*2=1-1/3^10=(3^10-1)/3^10

=>A=(3^10-1)/(2*3^10)

c: C=3/2+3/8+3/32+3/128+3/512

=>4C=6+3/2+...+3/128

=>3C=6-3/512

=>C=1023/512

d: A=1/2+...+1/256

=>2A=1+1/2+...+1/128

=>A=1-1/256=255/256

Đặt S=1+2+4+8+16+32+64+128=2⁰+2¹+2²+...+2⁷

2S=2¹+2²+2³+...+2⁸

2S-S=(2¹+2²+2³+...+2⁸)-(2⁰+2¹+2²+...+2⁷)

S=2⁸-2

Cho mình sửa lại xíu nhé:

2 + 4 + 16 + 32 + 64 + 128 + 256

=(2 + 128) + (4 + 16) + (8 + 32) + (64 + 256)

= 130 + 20 + 40 + 320 

=510

\(2+4+8+16+32+64+128+256\)

\(=\left(128+2\right)+\left(256+4\right)+\left(64+16\right)+\left(32+8\right)\)

\(=130+260+80+40\)

\(=390+120\)

\(=610\)

2 + 4 + 8 + 16 + 32 + 64 + 128 + 256

= (2 + 128) + (4 + 16) + (8 + 32) + (64 + 256)

= 200 + 20 + 40 + 320

= 580

b:3=1/2+1/4+1/8+1/16+1/32+1/64+1/128

[b:3]x2=1+1/2+1/4+1/8+1/16+1/32+1/64

[b:3]x2-[b:3]=1+1/2+1/4+1/8+1/16+1/32+1/64-1/2+1/4+1/8+1/16+1/32+1/64+1/128

b:3=1-1/128

b:3=127/128

b=127/128x3

b=381/128

B.2=\(3+\frac{3}{2}+\frac{3}{4}+\frac{3}{8}+\frac{3}{16}+\frac{3}{32}+\frac{3}{64}\)\(+\frac{3}{128}\)

B.2-B=\(\left(3+\frac{3}{2}+\frac{3}{4}+\frac{3}{8}+\frac{3}{16}+\frac{3}{32}+\frac{3}{64}+\frac{3}{128}\right)\).\(\left(\frac{3}{2}+\frac{3}{4}+\frac{3}{8}+\frac{3}{16}+\frac{3}{32}+\frac{3}{64}+\frac{3}{128}\right)\)

B=3-\(\frac{3}{128}\)

B=\(\frac{381}{128}\)

b:3=1/2+1/4+1/8+1/16+1/32+1/64+1/128

[b:3]x2=1+1/2+1/4+1/8+1/16+1/32+1/64

[b:3]x2-[b:3]=1+1/2+1/4+1/8+1/16+1/32+1/64-1/2+1/4+1/8+1/16+1/32+1/64+1/128

b:3=1-1/128

b:3=127/128

b=127/128x3

b=381/128

cho mình 

3(1/2+1/4+1/8+1/16.....1/128)

A=(1/2+1/4+1/8+1/16....1/128)

2A-A=A

2A=(1/2+1/4+1/8....1/128)*2

=1+1/2+1/4....1/64

2A-A=1+1/2+1/4+1/8....1/64-(1/2+1/4+1/8......1/128)

A=1-1/128=127/128

Đáp số:3*127/128=381/128