Вариант 4 1. Сократите дробь: a) $$rac{15x^4y^7}{25x^6y^4}$$; б) $$rac{a^2-25}{a^2-10a+25}$$

a) $$\frac{15x^4y^7}{25x^6y^4} = \frac{3 \cdot 5 \cdot x^4 \cdot y^4 \cdot y^3}{5 \cdot 5 \cdot x^4 \cdot x^2 \cdot y^4} = \frac{3y^3}{5x^2}$$ б) $$\frac{a^2-25}{a^2-10a+25} = \frac{(a-5)(a+5)}{(a-5)^2} = \frac{a+5}{a-5}$$