3) \(\frac{5x}{a-b}-\frac{2x}{b-a}=\)

Так как \(b-a=-(a-b)\), то \(\frac{2x}{b-a}=-\frac{2x}{a-b}\).

\(\frac{5x}{a-b}-\frac{2x}{b-a}=\frac{5x}{a-b}+\frac{2x}{a-b}=\frac{7x}{a-b}\).

Ответ: \(\frac{7x}{a-b}\).