2a-4分之3-a/(a+2-a-2分之5),
=(3-a)/2(a-2)÷[(a+2)(a-2)-5]/(a-2)
=(3-a)/2÷(a²-9)
=（3-a）/2÷[（a+3）（a-3）]
=-1/2(a+3)
=-1/2(-1/2+3)
=-1÷5
=-1/5
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