сократите дробь:
(36/x^2) - (x/x-6) + 6/x

(36х-216-х^3+6х^2-36х)/(x^2(х-6))=(6x^2-x^3-216)/x^2(x-6)=(x^2(6-x)-216)= -(x^2-216)(6-x)/(x^2(6-x))= -(x^2-216)/x^2