a) $$\frac{14a^3b^5}{21a^4b^6} = \frac{2 \cdot 7 \cdot a^3 \cdot b^5}{3 \cdot 7 \cdot a^4 \cdot b^6} = \frac{2}{3} \cdot \frac{1}{a} \cdot \frac{1}{b} = \frac{2}{3ab}$$
б) $$\frac{x^2 + x}{x^2} = \frac{x(x + 1)}{x^2} = \frac{x + 1}{x}$$
Ответ: a) $$\frac{2}{3ab}$$; б) $$\frac{x + 1}{x}$$