1\2+1\4+1\8+1\16+1\32+1\64+1\128=\(\frac{127}{128}\)
1/2+1/4+1/8+1/16+1/32+1/64+1/128=127/128
hok tốt
\(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\)\(+\frac{1}{128}\)
\(A=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+\frac{1}{2^5}+\frac{1}{2^6}\)\(+\frac{1}{2^7}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+\frac{1}{2^5}\)\(+\frac{1}{2^6}+\frac{1}{2^7}\)\(+\frac{1}{2^8}\)
\(\Rightarrow A-\frac{1}{2}A=\frac{1}{2}-\frac{1}{2^8}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2}.\left(1-\frac{1}{2^7}\right)\)
\(\Rightarrow A=1-\frac{1}{2^7}\)
tính nhanh p/s 1+ 5/4 + 5/8 + 5/16 + 5/32 + 5/64
