Выполни действия

1. \(\dfrac{5a}{x-y}-\dfrac{7a}{y-x}=\) [ ];
2. \(\dfrac{3x}{a-2b}+\dfrac{3y}{2b-a}=\) [ ];
3. \(\dfrac{2a-b}{a-b}-\dfrac{b}{b-a}=\) [ ].