\[\boxed{\text{893.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (6x - 1)(6x + 1) - 4x(9x + 2) = - 1\]
\[36x^{2} - 1 - 36x^{2} - 8x = - 1\]
\[- 8x = - 1 + 1\]
\[- 8x = 0\]
\[x = 0\]
\[Ответ:x = 0.\]
\[\textbf{б)}\ (8 - 9a)a = - 40 + (6 - 3a)(6 + 3a)\]
\[8a - 9a^{2} = - 40 + 36 - 9a^{2}\]
\[8a = - 4\]
\[a = - \frac{1}{2}\]
\[a = - 0,5\]
\[Ответ:a = - 0,5.\]