(x+3)/(x²+3)*((x+3)/(x-3)-(x-3)/(x+3))=
((х+3)*(х²+9+6х-х²+6х-9)/((х²+3)*(х+3)(х-3))=
12х/((х-3)(х²+3))
(x+3)/(x²+3)*((x+3)/(x-3)-(x-3)/(x+3))=
((х+3)*(х²+9+6х-х²+6х-9)/((х²+3)*(х+3)(х-3))=
12х/((х-3)(х²+3))