化简后求值：（a+3/a^2-4+a/6-a-a^2）除以4a+9/5a-10,其中x=8

[(a+3)/(a+2)(a-2)-a/(a+3)(a-2)]×5(a-2)/(4a+9)=[(a+3)/(a+2)-a/(a+3)] ×5/(4a+9)=[(a+3)²-a(a+2)]/(a+2)(a+3)×5/(4a+9)=(4a+9)/(a+2)(a+3)×5/(4a+9)=5/(a+2)(a+3)当a=8时原式=5/10×11=1/22