1/2+1/4+1/8+1/16+1/32+1/64

=(1/2+1/4+1/8)+(1/16+1/32+1/64)

=(4/8+2/8+1/8)+(4/64+2/64+1/64)

=7/8+7/64

=56/64+7/64

=63/64

           B =        \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) +  \(\dfrac{1}{16}\)  + \(\dfrac{1}{32}\) + \(\dfrac{1}{64}\) 

    2 x B   = 1 + \(\dfrac{1}{2}\)+ \(\dfrac{1}{4}\)  +  \(\dfrac{1}{8}\) +  \(\dfrac{1}{16}\)+ \(\dfrac{1}{32}\)

2 x B - B = 1 - \(\dfrac{1}{64}\)

           B = \(\dfrac{63}{64}\)

đặt `A= 1/2 + 1/4 + 1/8 + 1/16+ 1/32 + 1/64`

`=> 2A = 2(1/2 + 1/4 + 1/8 + 1/16+ 1/32 + 1/64)`

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

`=>A =2A -A =1+1/2 +1/4 +1/8+1/16 +1/32-1/2-1/4-1/8-1/16-1/32 -1/64`

`A = 1-1/64 = 64/64 -1/64 =63/64`

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

=> 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

Vậy: ...

voi lai phan so sau hon phan so truoc la 2 doi vi anh nhat linh a?

63/64 do ban oi oi!

qua don giai lop bon da hoc roi goi y cho 

buoc 1 : Dat A

buoc 2:nhan ca hai ve voi N

buoc 3: tru ca hai ve cho nhau

1/2 + 1/3 + 1/4 + 1/5 + 4/5 + 3/4 + 2/3 + 1/2

= (1/2 + 1/2) + (1/3 + 2/3) + (1/4 + 3/4) + (1/5 + 4/5)

= 1 + 1 + 1 + 1

= 4

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

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

\(A=1-\frac{1}{64}\)

\(A=\frac{63}{64}\)

\(B=\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)

\(3B=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)

\(3B-B=1-\frac{1}{243}\)

\(2B=\frac{242}{243}\)

\(B=\frac{242}{243}\div2\)

\(B=\frac{121}{243}\)

a.A=1/2+1/4+1/8+1/16+1/32+1/64

 A= \(\frac{1}{1\cdot2}+\frac{1}{2\cdot2}+\frac{1}{2\cdot4}+\frac{1}{4\cdot4}+\frac{1}{4\cdot8}+\frac{1}{8\cdot8}\)

= \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{4}+\frac{1}{4}-\frac{1}{8}+\frac{1}{8}-\frac{1}{8}\)

= 1 - 1/8 = 7/8

b.B=1/3+1/9+1/27+1/81+1/243

B= \(\frac{1}{1\cdot3}+\frac{1}{3\cdot3}+\frac{1}{3\cdot9}+\frac{1}{9\cdot9}+\frac{1}{9\cdot27}\)

= 1 - 1/27 = 26/27