Câu a:Đáp số 127/128

Câu b:Đáp số 1021/63

a) Đặt A= 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256 
2A= 2(1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256) 
     = 1+1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 
=>A =  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 
=1-1/256 
=255/256

b) = 18 - (19/21 + 8/9) = 18 - 113/63 = 1021/63

a) Đặt A= 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256 
2A= 2(1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 + 1/256) 
     = 1+1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128 
=>A =  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 
=1-1/256 
=255/256

b) sai đề

= 18 x \(\left(\frac{19.1010101}{21.1010101}+\frac{8.11111}{9.11111}\right)\)= 18 x ( \(\frac{19}{21}+\frac{8}{9}\)) = 9 x 2 ( \(\frac{57+56}{63}\))

= 9 x 2 x \(\frac{113}{63}\)=\(\frac{226}{7}\)

dũng làm chẳng  hiểu gì cả

= 18 ( 19/21 + 8/9)

= 18.113/63

=226/7 

\(=18x\frac{19x1010101}{21x1010101}+\frac{8x11111}{9x11111}=18x\frac{19}{21}+\frac{8}{9}\)

sao khong có kết quả hả bạn

\(18\cdot\left(\frac{19191919}{21212121}+\frac{88888}{99999}\right)\)

\(=18\cdot\left(\frac{19}{21}+\frac{8}{9}\right)\)

\(=18\cdot\frac{113}{63}\)

\(=\frac{678}{21}\approx32,286\)

55555

\(=18\times\left(\frac{19}{21}+\frac{8}{9}\right)=18\times\frac{113}{63}=\frac{226}{7}\)

=226/7

**** mình nha

\(18.\left(\frac{19191919}{21212121}+\frac{88888}{99999}\right)=18.\left(\frac{19}{21}+\frac{8}{9}\right)=18.\frac{113}{63}=\frac{226}{7}nha!!!!!\)

\(\frac{226}{7}\)

\(\frac{63.\left(19191919+88888\right)}{212121+99999}=\frac{63.\left(19191919+18181+70707\right)}{21212121+97979+2020}=\frac{63.\left(19200000+70707\right)}{21300000+2020}\)\(=\frac{63.19270707}{21302020}\)