Hey

I don't understand how to determine the domain of concave up versus concave down when the graph has two points of inflection.

For example

x^4 + 8x^3 + 18x^2 + 8

extreme points: -3, 0

(graph is high at -3 and low at 0)

Points of inflection: -3, -1

My textbook says the answer is

concave up (- infinity , -3) , ( -1, inifinity)

Concave down ( -3 , -1)