Сокращение дробей

a) $$rac{14a^4b}{49a^3b^2} = rac{2 cdot 7 cdot a^3 cdot a cdot b}{7 cdot 7 cdot a^3 cdot b cdot b} = rac{2a}{7b}$$

б) $$rac{3x}{x^2 + 4x} = rac{3x}{x(x + 4)} = rac{3}{x + 4}$$

в) $$rac{y^2 - z^2}{2y + 2z} = rac{(y - z)(y + z)}{2(y + z)} = rac{y - z}{2}$$