a/a^2+3a+2=a/(a+1)(a+2)=3a(a+1)/3(a+1)^2(a+2)
a/a^2+2a+1=a/(a+1)^2=3a(a+2)/3(a+1)^2(a+2)
-1/3a+6= -1/3(a+2)= -(a+1)^2/3(a+1)^2(a+2)