a) \frac{3ab}{12ac} = \frac{3 \cdot a \cdot b}{3 \cdot 4 \cdot a \cdot c} = \frac{b}{4c}
б) \frac{-4ax}{6bx^2} = \frac{-2 \cdot 2 \cdot a \cdot x}{2 \cdot 3 \cdot b \cdot x \cdot x} = -\frac{2a}{3bx}
в) \frac{(a + 2)^2}{3a + 6} = \frac{(a + 2)(a + 2)}{3(a + 2)} = \frac{a + 2}{3}
г) \frac{a^2 - 1}{a^2 - 2a + 1} = \frac{(a - 1)(a + 1)}{(a - 1)^2} = \frac{a + 1}{a - 1}