应该是y＝x³－3x²－9x＋11吧 是的话求解如下：求导,f'(x)=0得f'(x)＝3x²-6x-9=0解得x1=-1 x2=3令f’(x)＞0解得x＞3或x＜-1令f’(x)＜0,解得-1＜x＜3∴y=f(x)单调递增区间是（-∞,-1）∪（3,+∞）,单...