\(A=\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)...\left(1-\frac{1}{2003}\right)\left(1-\frac{1}{2004}\right)\)
\(A=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{2002}{2003}.\frac{2003}{2004}=\frac{1}{2004}\)
\(A=\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)...\left(1-\frac{1}{2004}\right)\)
\(\Rightarrow A=\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}...\frac{2002}{2003}\cdot\frac{2003}{2004}\)
\(\Rightarrow A=\frac{1\cdot2\cdot3...2003}{2\cdot3\cdot4...2004}=\frac{1}{2004}\)