Question

求函数f(x)=x^3-3x^2-9x+7的极值

Answer 1

f'(x)=3x^2-6x-9=3(x^2-2x-3)=3(x-3)(x+1)=0,得 x=3,-1

极大值为f(-1)=-1-3+9+7=12

极小值为f(3)=27-27-27+7=-20