А1. Сократите дробь: a) $$rac{12ab}{4a}$$; б) $$rac{3c(1-c)}{9c^2(c-1)}$$.

a) $$rac{12ab}{4a} = rac{3b}{1} = 3b$$ б) $$rac{3c(1-c)}{9c^2(c-1)} = rac{3c cdot (-1)(c-1)}{9c^2(c-1)} = rac{-3c}{9c^2} = -\frac{1}{3c}$$