\[\boxed{\mathbf{511}\mathbf{.}}\]
\[= \frac{\sin^{3}a \bullet \sin a - \cos^{4}a \bullet \cos a}{\cos a \bullet \sin a \bullet \left( \sin a + \cos a \right)} =\]
\[2)\ \frac{2\sqrt{2} \bullet \sin\left( a - \frac{\pi}{4} \right)}{\sin{2a}} =\]
\[= \frac{2\sin a - 2\cos a}{2\sin a \bullet \cos a} =\]
\[= \frac{\sin a - \cos a}{\sin a \bullet \cos a}\]
\[\frac{\sin a - \cos a}{\sin a \bullet \cos a} = \frac{\sin a - \cos a}{\sin a \bullet \cos a}\]
\[Что\ и\ требовалось\ доказать.\]