57. \(\dfrac{4x}{x^2-y^2}-\dfrac{4}{x-y}\)

Разложим: \(x^2-y^2=(x-y)(x+y)\).

\[\frac{4x}{(x-y)(x+y)}-\frac{4(x+y)}{(x-y)(x+y)}=\frac{4x-4x-4y}{x^2-y^2}.\]

Ответ: \(-\dfrac{4y}{x^2-y^2}\), \(x\ne\pm y\).