3. Сократите дробь: 4b+12. 1) a) b²-9 ; c²+c-6 6) 7c+21 ; 16-2x B) 8+7x-x² a²-16a+63 2) a) a²-81 ; y³+7y²-60y 6) 10y-50 ; 3+146-56 B) 3b-b² .

1. a) $$\frac{4b+12}{b^2-9} = \frac{4(b+3)}{(b-3)(b+3)} = \frac{4}{b-3}$$
2. б) $$\frac{c^2+c-6}{7c+21} = \frac{(c+3)(c-2)}{7(c+3)} = \frac{c-2}{7}$$
3. в) $$\frac{16-2x}{8+7x-x^2} = \frac{-2(x-8)}{-(x-8)(x+1)} = \frac{2}{x+1}$$
4. a) $$\frac{a^2-16a+63}{a^2-81} = \frac{(a-7)(a-9)}{(a-9)(a+9)} = \frac{a-7}{a+9}$$
5. б) $$\frac{y^3+7y^2-60y}{10y-50} = \frac{y(y^2+7y-60)}{10(y-5)} = \frac{y(y+12)(y-5)}{10(y-5)} = \frac{y(y+12)}{10}$$
6. в) $$\frac{3+14b-5b^2}{3b-b^2} = \frac{-(5b-1)(b-3)}{b(3-b)} = \frac{5b-1}{b}$$

Ответ:

1. a) $$\frac{4}{b-3}$$
2. б) $$\frac{c-2}{7}$$
3. в) $$\frac{2}{x+1}$$
4. a) $$\frac{a-7}{a+9}$$
5. б) $$\frac{y(y+12)}{10}$$
6. в) $$\frac{5b-1}{b}$$