Đặt A= $\frac{1}{2}$- $\frac{1}{4}$+ $\frac{1}{8}$- $\frac{1}{16}$+ $\frac{1}{32}$- $\frac{1}{64}$
2A= 1- $\frac{1}{2}$- $\frac{1}{4}$+ $\frac{1}{8}$- $\frac{1}{16}$+ $\frac{1}{32}$
2A- A= 1- $\frac{1}{64}$
A= $\frac{63}{64}$
Vì $\frac{63}{64}$< $\frac{1}{3}$
nên $\frac{1}{2}$- $\frac{1}{4}$+ $\frac{1}{8}$- $\frac{1}{16}$+ $\frac{1}{32}$- $\frac{1}{64}$< 3
Vậy $\frac{1}{2}$- $\frac{1}{4}$+ $\frac{1}{8}$- $\frac{1}{16}$+ $\frac{1}{32}$- $\frac{1}{64}$< 3
CHO MIK CTLHN NHÉ
