Объяснение:
f'(x)=[1*(9-x^2)-x*(-2x)] /(9-x^2)^2=(9-x^2+2x^2) /(9-x^2)^2=(9+x^2) /(9-x^2)^2,
9-x^2 не=0. x^2 не=9, х не=3 и х не=-3,
D(f)= (-~;-3), (-3;3), (3;+~)
