\(\frac{1}{2}\times\frac{2}{3}\)

\(=\frac{3}{6}\times\frac{4}{6}\)

\(=\frac{12}{36}\)

\(=\frac{1}{3}\)

bít làm mà mk ko bít cách trình bày

\(=\frac{1}{2^1}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\)

\(=2\left(\frac{1}{2^1}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\right)-\left(\frac{1}{2^1}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\right)\)

\(=2+\frac{1}{2^1}+\frac{1}{2^2}+...+\frac{1}{2^6}-\frac{1}{2^1}-\frac{1}{2^2}-\frac{1}{2^3}-...-\frac{1}{2^7}\)

\(=2-\frac{1}{2^7}=\frac{255}{128}\)