\[\boxed{\text{832.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ 18a + (a - 9)^{2} = 18a + a² -\]
\[- 18a + 81 = a^{2} + 81\]
\[\textbf{б)}\ (5x - 1)^{2} - 25x^{2} = 25x^{2} -\]
\[- 10x + 1 - 25x^{2} = - 10x + 1\]
\[\textbf{в)}\ 4x² - (2x - 3)^{2} = 4x^{2} -\]
\[- \left( 4x^{2} - 12x + 9 \right) =\]
\[= 4x^{2} - 4x^{2} + 12x - 9 =\]
\[= 12x - 9\]
\[\textbf{г)}\ (a + 2b)^{2} - 4b^{2} = a^{2} +\]
\[+ 4ab + 4b^{2} - 4b^{2} = a^{2} + 4ab\]