A=\(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{256}\)

A=\(\left(1-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{8}\right)+...+\left(\frac{1}{128}-\frac{1}{256}\right)\)

A=\(1-\frac{1}{256}\)

A=\(\frac{255}{256}\)

A = 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256

2A = 1/2 x 2 + 1/4 x 2 + 1/8 x 2 + 1/16 x 2 +1/32 x 2 + 1/64 x 1/128 + 1/256 x 2

2A = 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128

2A - A = ( 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 ) - ( 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256 )

A = 1 - 1/256

A = 255/256

A=$\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{256}$

A=$\left(1-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{8}\right)+...+\left(\frac{1}{128}-\frac{1}{256}\right)$

A=$1-\frac{1}{256}$

A=$\frac{255}{256}$

\(=\frac{32+16+8+4+2+1}{64}=\frac{63}{64}\)

câu 1 . 125

câu 2 .97

k mình nha bn

15/16

P=1/2+1/4+...+1/256

2P=2.(1/2+1/4+...+1/256)

2P-P=(1+1/2+...+1/128)-(1/2+1/4+...+1/256)

P= 1- 1/256

P= 255/256

chắc chắn đúng.

nhớ **** cho mình nha

*Tham khảo 

1/2 + 1/4+ 1/8+ 1/16 + 1/32 + 1/64 + 1/128 + 1/256 + 1/512
= 1 – 1/2 + 1/2- 1/4 + 1/4 – 1/8 + 1/8 – 1/16 + 1/16 – 1/32 + 1/32 – 1/64 + 1/64 – 1/128 + 1/128 – 1/256 – 1/256 – 1/512
= 1 – 1/512

= 511/512 .

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