73. \(\dfrac{a-c}{a-c}-\dfrac{a-c}{a+c}\)

ОДЗ: \(a\ne c\), \(a\ne -c\).

\[\dfrac{a-c}{a-c}-\dfrac{a-c}{a+c}=1-\dfrac{a-c}{a+c}=\dfrac{a+c-a+c}{a+c}.\]

\[\dfrac{2c}{a+c}.\]

Ответ: \(\dfrac{2c}{a+c}\), \(a\ne\pm c\).