Преобразуем выражение.

a)

$$\frac{x^2}{x^2 - 16} - \frac{8(x - 2)}{x^2 - 16} = \frac{x^2 - 8(x - 2)}{x^2 - 16} = \frac{x^2 - 8x + 16}{x^2 - 16} = \frac{(x - 4)^2}{(x - 4)(x + 4)} = \frac{x - 4}{x + 4}$$

б)

$$\frac{64 - 2ab}{(a - 8)^2} + \frac{2ab - a^2}{(8 - a)^2} = \frac{64 - 2ab}{(a - 8)^2} + \frac{2ab - a^2}{(a - 8)^2} = \frac{64 - 2ab + 2ab - a^2}{(a - 8)^2} = \frac{64 - a^2}{(a - 8)^2} = \frac{(8 - a)(8 + a)}{(a - 8)^2} = \frac{-(a - 8)(8 + a)}{(a - 8)^2} = -\frac{a + 8}{a - 8} = \frac{a + 8}{8 - a}$$