\[\begin{array}{l}
b)\,\,B = \left| {\frac{3}{5} - x} \right| + \frac{1}{9}\\
Vi\,\,\,\left| {\frac{3}{5} - x} \right| \ge 0\,\,\,\forall x\\
\Rightarrow \,\,\left| {\frac{3}{5} - x} \right| + \frac{1}{9} \ge \frac{1}{9}\\
Dau\,\, = \,\,xay\,\,ra \Leftrightarrow \frac{3}{5} - x = 0 \Leftrightarrow x = \frac{3}{5}.\\
Vay\,\,Min\,A = \frac{1}{9}\,\,\,khi\,\,\,\,x = \frac{3}{5}.\\
c)\,\,\,C = \,\,\frac{{2004}}{{2005}} - \left| {x - \frac{3}{5}} \right|\\
Vi\,\,\,\left| {x - \frac{3}{5}} \right| \ge 0\,\,\,\forall x\\
\Rightarrow - \left| {x - \frac{3}{5}} \right| \le 0\\
\Rightarrow \frac{{2004}}{{2005}} - \left| {x - \frac{3}{5}} \right| \le \frac{{2004}}{{2005}}\\
Dau\,\, = \,\,xay\,\,ra \Leftrightarrow x - \frac{3}{5} = 0 \Leftrightarrow x = \frac{3}{5}\\
Vay\,\,Max\,C = \frac{{2004}}{{2005}}\,\,khi\,\,x = \frac{3}{5}.\\
d)\,\,\,D = - \frac{{2003}}{{2002}} - \left| {\frac{{2000}}{{2001}} - 2x} \right|\\
Vi\,\,\,\,\,\left| {\frac{{2000}}{{2001}} - 2x} \right| \ge 0\\
\Rightarrow - \,\left| {\frac{{2000}}{{2001}} - 2x} \right| \le 0\\
\Rightarrow - \frac{{2003}}{{2002}} - \left| {\frac{{2000}}{{2001}} - 2x} \right| \le - \frac{{2003}}{{2002}}\\
Dau\,\, = \,\,xay\,\,ra \Leftrightarrow \frac{{2000}}{{2001}} - 2x = 0 \Leftrightarrow x = \frac{{1000}}{{2001}}\\
Vay\,\,MaxD = - \frac{{2003}}{{2002}}\,\,\,khi\,\,\,x = \frac{{1000}}{{2001}}.
\end{array}\]
