a) $$rac{39x^3y}{26x^2y^2} = \frac{3 cdot 13 cdot x^2 cdot x cdot y}{2 cdot 13 cdot x^2 cdot y cdot y} = \frac{3x}{2y}$$
б) $$rac{5y}{y^2-2y} = \frac{5y}{y(y-2)} = \frac{5}{y-2}$$
в) $$rac{3a-3b}{a^2-b^2} = \frac{3(a-b)}{(a-b)(a+b)} = \frac{3}{a+b}$$