(6а+3)/a^2-18a + 6a-3/a^2+18a) умножить на a^2-324/a^2+9 !

(6a+3)/[a(a-18)]+(6a-3)/[a(a+18)]=[(6a+3)(a+18)+(6a-3)(a-18)]/[a(a²-324)]=
=(6a²+108a+3a+54+6a²-108a-3a+54)/[a(a²-324)]=(12a²+108)/[a(a²-324)]=
=12(a²+9)/[a(a²-324)]

12(a²+9)/[a(a²-324)]*(a²-324)/(a²+9)=12/a