решаю по частям
1) 2m/(4m^2-12m+9)-3/(4m^2-9)=2m/(2m-3)^2-3/(2m-3)(2m+3)=2m(2m+3)-3(2m-3)/((2m-3)^2(2m+3))4m^2+6m-6m+9/((2m-3)^2(2m+3))=4m^2+9/((2m-3)^2(2m+3))
4m^2+9/((2m-3)^2(2m+3))*(8m^3-18m)/(4m^2+9)=2m(4m^2-9)/((2m-3)^2(2m+3))=
2m(2m-3)(2m+3)/(2m-3^2(2m+3)=2m/(2m-3)
2m/(2m-3)-3/(2m-3)=2m-3/(2m-3)=1
2) a^2+a-12/(a^3-27)-1/(a^2+3a+9)=a^2+a-12/(a-3)(a^2+3a+9)-1/(a^2+3a+9)=
a^2+a-12-a+3/(a-3)(a^2+3a+9)=a^2-9/(a-3)(a^2+3a+9)=a+3/(a^2+3a+9)
a+9/(a+3)=a^2+3a+9/(a+3)
a+3/(a^2+3a+9)*((a^2+3a+9)/(a+3))=1