$\frac{5x + 3}{x^2 - 16} + \frac{6x - 1}{16 - x^2} = \frac{5x + 3}{x^2 - 16} - \frac{6x - 1}{x^2 - 16} = \frac{5x + 3 - (6x - 1)}{x^2 - 16} = \frac{5x + 3 - 6x + 1}{x^2 - 16} = \frac{-x + 4}{x^2 - 16} = \frac{-(x - 4)}{(x - 4)(x + 4)} = \frac{-1}{x + 4} = -\frac{1}{x + 4}$
при x = −4,1:
$-\frac{1}{x + 4} = -\frac{1}{-4,1 + 4} = -\frac{1}{-0,1} = \frac{1}{\frac{1}{10}} = 10$

$\frac{a^2 + a}{a^2 - 9} - \frac{7a - 9}{a^2 - 9} = \frac{a^2 + a - (7a + 9)}{a^2 - 9} = \frac{a^2 + a - 7a - 9}{a^2 - 9} = \frac{a^2 - 6a - 9}{a^2 - 9} = \frac{(a - 3)^2}{(a - 3)(a + 3)} = \frac{a - 3}{a + 3}$
при a = 7:
$\frac{a - 3}{a + 3} = \frac{7 - 3}{7 + 3} = \frac{4}{10} = 0,4$