Question

利用二阶导数，求函数极值

Answer 1

y=x^3-3x^2-9x-5
y'=3x^2-6x-9
y'=0
x^2-2x-3=0
(x-3)(x+1)=0
x=3 or -1
y''=6x-6
y''(3)>0 (min)
y''(-1) <0 (max)
min f(x) = f(3)=27-27-27-5 =-32
max f(x) = f(-1) =-1-3+9-5=0