r) x^2-49/8x^3 * x/7-x ;

r) $$\frac{x^2-49}{8x^3} \cdot \frac{x}{7-x} = \frac{(x-7)(x+7)}{8x^3} \cdot \frac{x}{-(x-7)} = \frac{x(x-7)(x+7)}{-8x^3(x-7)} = -\frac{x+7}{8x^2}$$

Ответ: $$\frac{-(x+7)}{8x^2}$$