3) x²-25 x²-36; x²-6x x²+5x

3) $$\frac{x^2 - 25}{x^2 - 6x} \cdot \frac{x^2 - 36}{x^2 + 5x} = \frac{(x-5)(x+5) \cdot (x-6)(x+6)}{x(x-6) \cdot x(x+5)} = \frac{(x-5)(x+6)}{x^2}$$

Ответ: $$\frac{(x-5)(x+6)}{x^2}$$