f(x)=2x^2-lnx定义域为x＞0f'(x)=4x-1/x令f'(x)=0,4x-1/x=0得x=1/2或-1/2因为x＞0,所以极值取x=1/2f"(x)=4+1/x^2,当x=1/2时f"(1/2)=8＞0,所以x=1/2为极小值点f（x）在（0,1/2]区间单调减少,在[1/2,正无穷)区间单调增...