\[\boxed{\text{75\ (75).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ ab + 3b - 5a - 15 =\]
\[= b(a + 3) - 5 \cdot (a + 3) =\]
\[= (a + 3)(b - 5)\]
\[\textbf{б)}\ 2xy - y + 8x - 4 =\]
\[= y(2x - 1) + 4 \cdot (2x - 1) =\]
\[= (2x - 1)(y + 4)\]
\[\boxed{\text{75.\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[\textbf{а)}\ 5\sqrt{x} = 1\]
\[\sqrt{x} = \frac{1}{5}\]
\[x = \frac{1}{25} = 0,04.\]
\[Ответ:\ x = 0,04.\]
\[\textbf{б)}\ \sqrt{x - 4} = 15\]
\[x - 4 = 225\]
\[x = 229.\]
\[Ответ:x = 229.\]