Question

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

A = ....

Giúp mk nha ! đúng mk sẽ tick cho ^_^ !

Answer 1

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

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

A = 217/218 tick đúng nha

Answer 2

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

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

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

\(A=\left(\frac{1}{2}-\frac{1}{256}\right)\times2=1-\frac{1}{128}=\frac{127}{128}\)

Answer 3

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

 

=1-1/2+1/2-1/4+1/4-1/8+ ... +1/64-1/128

=127/128

TICK