\[\boxed{\text{1014.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (a + 8)^{2} -\]
\[- 2 \cdot (a + 8)(a - 2) +\]
\[+ (a - 2)^{2} =\]
\[= a^{2} + 16a + 64 - 2 \cdot\]
\[\cdot \left( a^{2} - 2a + 8a - 16 \right) + a^{2} -\]
\[- 4a + 4 =\]
\[= 2a^{2} + 12a + 68 - 2a^{2} -\]
\[- 12a + 32 = 100\]
\[\textbf{б)}\ \ (y - 7)^{2} - 2 \cdot\]
\[\cdot (y - 7)(y - 9) + (y - 9)^{2} =\]
\[= y^{2} - 14y + 49 - 2 \cdot\]
\[\cdot \left( y^{2} - 9y - 7y + 63 \right) + y^{2} -\]
\[- 18y + 81 =\]
\[= 2y^{2} - 32y + 130 - 2y^{2} +\]
\[+ 32y - 126 = 4\]