Ответ:
а) \[\frac{2x-y-1}{4x^3}-\frac{3y-x}{6x^2}=\frac{3(2x-y-1)-2x(3y-x)}{12x^3}=\frac{2x^2-6xy+6x-3y-3}{12x^3}.\]
б) \[\frac{1-b^2}{3ab}+\frac{2b^3-1}{6ab^2}=\frac{2b(1-b^2)+2b^3-1}{6ab^2}=\frac{2b-1}{6ab^2}.\]
в) \[\frac{1}{3a^3}-\frac{2}{5a^3}=\frac{5-6}{15a^3}=-\frac{1}{15a^3}.\]
г) \[\frac{b^2}{6x^5}-\frac{b}{3x^6}=\frac{b^2x-2b}{6x^6}=\frac{b(bx-2)}{6x^6}.\]
