Выполни вычитание:
3. a^2/a^2-25 - a/a-5
4. 20x^2/4x-7 - 5x

3. a^2/(a^2-25) - a/(a-5) = a^2/(a+5)(a-5) - a/(a-5) = a^2/(a+5)(a-5) - a(a+5)/(a+5)(a-5) = (a^2- a^2 - 5a)/(a+5)(a-5) =-5a/(a^2-25)

4. 20x^2/(4x-7) - 5x = 20x^2/(4x-7) - 5x(4x-7)/(4x-7) = (20x^2 - 5x(4x-7))/(4x-7) = (20x^2 - 20x^2 + 35x)/(4x-7) = 35x/(4x-7)