\[\boxed{\text{943.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (a - 1)\left( a^{2} + 1 \right)(a + 1) -\]
\[- \left( a^{2} - 1 \right)^{2} - 2 \cdot \left( a^{2} - 3 \right) =\]
\[= \left( a^{2} - 1 \right)\left( a^{2} + 1 \right) -\]
\[- \left( a^{4} - 2a^{2} + 1 \right) - 2a^{2} + 6 =\]
\[= a^{4} - 1 - a^{4} + 2a^{2} -\]
\[- 1 - 2a^{2} + 6 = 4\]
\[\textbf{б)}\ \left( a^{2} - 3 \right)^{2} -\]
\[- (a - 2)\left( a^{2} + 4 \right)(a + 2) -\]
\[- 6 \cdot \left( 5 - a^{2} \right) =\]
\[= \left( a^{4} - 6a^{2} + 9 \right) -\]
\[- \left( a^{2} - 4 \right)\left( a^{2} + 4 \right) -\]
\[- 30 + 6a^{2} =\]
\[= a^{4} - 6a^{2} + 9 - a^{4} + 16 -\]
\[- 30 + 6a^{2} = - 5\]