1、对函数求导,得 f'(x)=x-a/x^2当x=1时,f(x)取得极值,则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,∴只有当x=1时,f'(x)=0当x≥1时,f'(x)≥0,函数单调递增当x≤1时,f'(x)≤0,函数单调递减