5. $$ \frac{10x^2y^4(c-d)}{20xy^5(d-c)} = \frac{10x^2y^4(c-d)}{-20xy^5(c-d)} = \frac{x}{-2y} = -\frac{x}{2y} $$
Ответ: $$\frac{-x}{2y}$$