Question

f（x）=2x的三次方-3x的平方-12x+8 怎样求函数fx的单调区间？

Answer 1

f(x)=2x^3-3x^2-12x+8

f'(x) = 6x^2-6x-12=0

x^2-x-2=0

(x-2)(x+1)=0

x= 2 or -1

f''(x) = 12x-6

f''(-1) 0 (min)

f(x)的单调区间

增加: (-∞, -1] or [2,+∞)

减小: [-1,2]...