3) x²-49/x²+9x * x²-81/x²-7x;

3) $$\frac{x^2-49}{x^2+9x} \cdot \frac{x^2-81}{x^2-7x} = \frac{(x-7)(x+7)}{x(x+9)} \cdot \frac{(x-9)(x+9)}{x(x-7)} = \frac{(x+7)(x-9)}{x^2} = \frac{x^2 - 9x + 7x - 63}{x^2} = \frac{x^2 - 2x - 63}{x^2}$$

Ответ: (x²-2x-63)/x²