当a=84时,求(a^2-9)分之(a-4) ÷ (a-3)分之1 × (a^2-8a+16)分之【(a+3)(a-1)】的值

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当a=84时,求(a^2-9)分之(a-4)÷(a-3)分之1×(a^2-8a+16)分之【(a+3)(a-1)】的值当a=84时,求(a^2-9)分之(a-4)÷(a-3)分之1×(a^2-8a+1

当a=84时,求(a^2-9)分之(a-4) ÷ (a-3)分之1 × (a^2-8a+16)分之【(a+3)(a-1)】的值
当a=84时,求(a^2-9)分之(a-4) ÷ (a-3)分之1 × (a^2-8a+16)分之【(a+3)(a-1)】的值

当a=84时,求(a^2-9)分之(a-4) ÷ (a-3)分之1 × (a^2-8a+16)分之【(a+3)(a-1)】的值
原式=[(a-4)/(a²-9)]÷[1/(a-3)]×[(a+3)(a-3)]/(a²-8a+16)
={(a-4)/[(a+3)(a-3)]}×(a-3)×[(a+3)(a-3)]/(a-4)²
=[(a-4)/(a+3)]×[(a+3)(a-3)]/(a-4)²
=(a-3)/(a-4)
当a=84时
原式=(84-3)/(84-4)
=81/80