\[\boxed{\mathbf{1326}\mathbf{.}}\]
\[1)\ (a - b)x = a^{2} + (a + b)x\]
\[ax - bx = a^{2} + ax + bx\]
\[a^{2} + ax - ax + bx + bx = 0\]
\[a^{2} + 2bx = 0\]
\[2bx = - a^{2}\]
\[x = - \frac{a^{2}}{2b}.\]
\[Ответ:\ \ x = - \frac{a^{2}}{2b}.\]
\[2)\ a^{2}x = a + b + b^{2}x\]
\[a^{2}x - b^{2}x = a + b\]
\[x \bullet \left( a^{2} - b^{2} \right) = a + b\]
\[x = \frac{a + b}{(a - b)(a + b)} = \frac{1}{a - b}.\]
\[Ответ:\ \ \frac{1}{a - b}.\]