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對f(x)求導,可得f‘(x)=1-a/x可知,當x=a時可取最小值(可有f’(x)的取值變化得知).所以f(a)最小值為a-1-alna,只要最小值≥0恒成立,那麼f(x)≥0恒成立.再由f(a)對a求導,則有f‘(a)=-lna,所以a=1時又可取最小值,f(a)…
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