Question

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

  a bang bao nhieu?

 

Answer 1

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

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

\(A=1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{128}\)

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

\(A=1-\frac{1}{256}\)\(A=\frac{255}{256}\)

Answer 2

Mẫu số chung là 256.

1/2=128/256 ; 1/4=64/256 ; 1/8=32/256 ; 1/16=6/256 ; 1/32=8/256 ; 1/64=4/256 ; 1/128=2/256 .1/256 giữ nguyên .

a=128+64+32+6+8+4+2+1/256

a=245/256