CSSA 1985 geometrical applications of differentiation (1 Viewer)

[Amina]

hey guys so I'm doing a geometrical applications of differentiation question from the CSSA 1985 paper and it goes like this:

"find the values of x for which the curve y=2x^3 - 3x^2 - 12x +6 rises with downward concavity"
and the answer is x≤-1
im not entirely sure how this is the answer and would like some help, because I'm getting a different answer. is the answer x≤-1 wrong?
thanks for ur help

 

[tywebb]

y'=6x²-6x-12>0 and y''=12x-6<0 have solution x<-1.

So maybe it should be x<-1 not x≤-1.