[(a+3)/(a^2-4)+a/(6-a-a^2)]除以(4a+9)/(5a-10)先化简= [(a+3)/(a+2)(a-2)]-a/(a+3)(a-2)除以(4a+9)/(5a-10)通分 （a+2）（a-2）(a+3)=[(a+3)^2 - a(a+2)]/（a+2）（a-2）(a+3)除以(4a+9)/(5a-10)先化简,再约分 =（...