Question

求函数f(x)=2x三次方-6x的平方-18x-7的单调区间？

Answer 1

对该函数求导：f'(x)=6x�0�5-12x-18令f'(x)=0解得：x=-1或3因为f'(x)=6x�0�5-12x-18是开口向上的所以x属于（-无穷，-1）时，f'(x)大于零，f(x)在该区间单调递增x属于（-1，3）时，f'(x)小于零，f(x)在该区间单调递减x属于（3，+无穷）时，f'(x)大于零，f(x)在该区间单调递增

Answer 2

f'(x)=6x^2-12x-18>0
x>3 x<-1
所以x>3或 x<-1时递增
－1<=x<=3时递减