Х3- 5х2-9х+45/(х-5)(х+3)
((x^3-5x^2)-(9x-45))/(x-5)(x+3)=(x^2(x-5)-9(x-5))/(x-5)(x+3)=(x-5)(x^2-9)/(x-5)(x+3)=(x^2-9)/(x+3)=(x-3)(x+3)/(x+3)=x-3