f(x)=lnx-x² +x定义域x＞0f′(x) = 1/x-2x+1 = -(2x²-x-1)/x = -(2x+1)(x-1)/xx＜1时↑，x＞1时↓x=1时有极大值f(1) = ln1-1²+1 = 0
