\[\boxed{\mathbf{2.}\mathbf{354}}\]
\[\textbf{а)}\ \left( \frac{2}{5} \right)^{2} = \frac{4}{25} = \frac{16}{100} = 0,16.\]
\[\textbf{б)}\ \left( \frac{3^{\backslash 3}}{4} - \frac{2^{\backslash 4}}{3} \right)^{2} =\]
\[= \left( \frac{9}{12} - \frac{8}{12} \right)^{2} = \left( \frac{1}{12} \right)^{2} = \frac{1}{144}.\]
\[\textbf{в)}\ \left( \frac{1}{2} \right)^{2} - \left( \frac{1}{4} \right)^{2} = \frac{1^{\backslash 4}}{4} - \frac{1}{16} =\]
\[= \frac{4}{16} - \frac{1}{16} = \frac{3}{16}.\]