$\frac{7}{2a - 4} - \frac{12}{a^2 - 4} - \frac{3}{a + 2} = \frac{7}{2(a - 2)} - \frac{12}{(a - 2)(a + 2)} - \frac{3}{a + 2} = \frac{7(a + 2) - 2 * 12 - 2 * 3(a - 2)}{2(a - 2)(a + 2)} = \frac{7a + 14 - 24 - 6a + 12}{2(a - 2)(a + 2)} = \frac{a + 2}{2(a - 2)(a + 2)} = \frac{1}{2(a - 2)}$
при a = 5:
$\frac{1}{2(a - 2)} = \frac{1}{2(5 - 2)} = \frac{1}{2 * 3} = \frac{1}{6}$

$\frac{2c + 3}{2c^2 - 3c} + \frac{2c - 3}{2c^2 + 3c} - \frac{16c}{4c^2 - 9} = \frac{2c + 3}{с(2с - 3)} + \frac{2c - 3}{с(2с + 3)} - \frac{16c}{(2с - 3)(2с + 3)} = \frac{(2c + 3)(2c + 3) + (2c - 3)(2c - 3) - 16c * c}{c(2с - 3)(2с + 3)} = \frac{(2c + 3)^2 + (2c - 3)^2 - 16c^2}{c(2с - 3)(2с + 3)} = \frac{4c^2 + 12c + 9 + 4c^2 - 12c + 9 - 16c^2}{c(2с - 3)(2с + 3)} = \frac{-8c^2 + 18}{c(2с - 3)(2с + 3)} = \frac{-(8c^2 - 18)}{c(2с - 3)(2с + 3)} = \frac{-(8c^2 - 18)}{c(2с - 3)(2с + 3)} = \frac{-2(4c^2 - 9)}{c(4c^2 - 9)} = \frac{-2}{c}$
при c = −0,8:
$\frac{-2}{c} = \frac{-2}{-0,8} = \frac{2}{\frac{8}{10}} = 2 * \frac{5}{4} = \frac{5}{2} = 2,5$

$\frac{m^2 + 16n^2}{m^2 - 16n^2} - \frac{m + 4n}{2m - 8n} = \frac{m^2 + 16n^2}{(m - 4n)(m + 4n)} - \frac{m + 4n}{2(m - 4n)} = \frac{2(m^2 + 16n^2) - (m + 4n)(m + 4n)}{2(m - 4n)(m + 4n)} = \frac{2m^2 + 32n^2 - (m + 4n)^2}{2(m - 4n)(m + 4n)} = \frac{2m^2 + 32n^2 - (m^2 + 8n + 16n^2)}{2(m - 4n)(m + 4n)} = \frac{2m^2 + 32n^2 - m^2 - 8n - 16n^2}{2(m - 4n)(m + 4n)} = \frac{m^2 - 8n + 16n^2}{2(m - 4n)(m + 4n)} = \frac{(m - 4n)^2}{2(m - 4n)(m + 4n)} = \frac{m - 4n}{2(m + 4n)}$
при m = 3, n = 0,5:
$\frac{m - 4n}{2(m + 4n)} = \frac{3 - 4 * 0,5}{2(3 + 4 * 0,5)} = \frac{3 - 2}{2(3 + 2)} = \frac{1}{2 * 5} = \frac{1}{10} = 0,1$