\[\boxed{\mathbf{471}\mathbf{.}}\]
\[= - \frac{1}{2}\left( \sin a - \cos a \right)^{2} + \frac{1}{2} \bullet 1 =\]
\[= - \frac{1}{2} \bullet {0,6}^{2} + \frac{1}{2} =\]
\[= - \frac{1}{2} \bullet \left( \frac{6}{10} \right)^{2} + \frac{1}{2} =\]
\[= - \frac{1}{2} \bullet \left( \frac{3}{5} \right)^{2} + \frac{1}{2} = - \frac{1}{2} \bullet \frac{9}{25} + \frac{1}{2} =\]
\[= - \frac{9}{50} + \frac{25}{50} = \frac{16}{50} = \frac{8}{25}.\]