1、對(duì)函數(shù)求導(dǎo),得 f'(x)=x-a/x^2當(dāng)x=1時(shí),f(x)取得極值,則f'(1)=0=1-a/1 => a=1
2、f'(x)=x-1/x^2=(x^3-1)/x^2=(x-1)(x^2+x+1)/x^2∵x^2+x+1=(x+1/2)^2+3/4>0,x^2>0,∴只有當(dāng)x=1時(shí),f'(x)=0當(dāng)x≥1時(shí),f'(x)≥0,函數(shù)單調(diào)遞增當(dāng)x≤1時(shí),f'(x)≤0,函數(shù)單調(diào)遞減