a=2时,f(x)=2x+2/x-3lnx
f'(x)=2-2/x^2-3/x
令f'(x)=0 即2(x^2)-3x-2=0 x=2或x=-1/2
又因为
f''(x)=4/x^3+3/x^2
f''(2)>0 f''(-1/2)