f(x)=ax^2+blnx
f'(x)=2ax+b/x
x=1
f'(1)=2a+b=0
f(1)=a=1
b=-2
f'(x)=2x-2/x(x>0)
f'(x)>0
2x^2-2>0
x>1
[1,R)单调增
(0,1)单调减