Ответ:

3/a + (a-3)/(a + 5) = (3*(a + 5) + a(a - 3)) /a (a + 5) = (3a + 15 +a^2 - 3a)/a(a + 5) =

=(a^2 + 15)/a(a + 5)

2) (2x^2)/(x^2 - 4) - 2x/(x + 2) = (2x^2 - 2x(x - 2))/(x^2 - 4) =

= (2x^2 - 2x^2 + 4x)/(x^ - 4) = 4x/(x^2 - 4)

3) 7a/(a - b) - 7 = (7a - 7(a - b))/(a - b) = (7a - 7a + 7b)/(a - b) = 7b/(a - b)