对y求导：y'=(x^3-6x^2+9x+1)'
=(x^3)'+(-6x^2)'+(9x)'+1'
=3x^2-6*2x+9+0
=3x^2-12x+9
求凹凸区间及拐点最好还要求二阶导数.
y''=6x-12 拐点：y''=0 6x-12=0 => x=2 y=8-24+18+1=3
当x