$(\frac{a^2}{a + 1} - \frac{a^3}{a^2 + 2a + 1}) : (\frac{a}{a + 1} - \frac{a^2}{a^2 - 1}) = (\frac{a^2}{a + 1} - \frac{a^3}{(a + 1)^2}) : (\frac{a}{a + 1} - \frac{a^2}{(a - 1)(a + 1)}) = \frac{a^2(a + 1) - a^3}{(a + 1)^2} : \frac{a(a - 1) - a^2}{(a - 1)(a + 1)} = \frac{a^3 + a^2 - a^3}{(a + 1)^2} : \frac{a^2 - a - a^2}{(a - 1)(a + 1)} = \frac{a^2}{(a + 1)^2} * \frac{(a - 1)(a + 1)}{-a} = \frac{-a(a - 1)}{a + 1} = \frac{a - a^2}{a + 1}$
при a = −3:
$\frac{-3 - (-3)^2}{-3 + 1} = \frac{-3 - 9}{-2} = \frac{-12}{-2} = 6$

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