lim[(3n^2+cn+1)/(an^2+bn)-4n]=lim[(3n^2+cn+1-4an^3-4bn^2)/(an^2+bn)]则-4a=0 即a=0极限化成lim[(3n^2+cn+1-4bn^2)/(bn)]则3-4b=0 即b=3/4再化成lim[(4/3)*(cn+1)/n]=4c/3=5则c=15/4即a=0 b=3/4 c=15/4...