3) \(\dfrac{4}{x-3}-\dfrac{1}{x+3}\)

Общий знаменатель: \((x-3)(x+3)=x^2-9\).

\[\dfrac{4}{x-3}-\dfrac{1}{x+3}=\dfrac{4(x+3)-(x-3)}{(x-3)(x+3)}=\dfrac{4x+12-x+3}{x^2-9}=\dfrac{3x+15}{x^2-9}=\dfrac{3(x+5)}{x^2-9}.\]

ОДЗ: \(x\ne3\), \(x\ne-3\).

Ответ: \(\dfrac{3(x+5)}{x^2-9}\).