Сократите дробь: a) $$rac{-21b^2y^2}{-28by}$$ b) $$rac{17x^{n+1}}{51x^{n+4}}$$ c) $$rac{a^2-49}{a^2-14a+49}$$

a) $$rac{-21b^2y^2}{-28by} = rac{3by}{4}$$ Ответ: $$\frac{3by}{4}$$ b) $$rac{17x^{n+1}}{51x^{n+4}} = rac{17x^{n+1}}{17 cdot 3 cdot x^{n+1} cdot x^3} = rac{1}{3x^3}$$ Ответ: $$\frac{1}{3x^3}$$ c) $$rac{a^2-49}{a^2-14a+49} = rac{(a-7)(a+7)}{(a-7)^2} = rac{a+7}{a-7}$$ Ответ: $$\frac{a+7}{a-7}$$