【2012a/(a²-4a+4)】÷【（2a+4)/(a²-4)+1】=【2012a/(a-2）²】÷【2(a+2)/(a+2)(a-2)+1】=【2012a/(a-2）²】÷【2/(a-2)+1】=【2012a/(a-2）²】÷【a/(a-2)】=【2012a/(a-2）²】*(a-2)/a=2012/(a-2)当a=3时，原式=2012
