# How do you determine whether the function #f(x) = -x^4-9x^3+2x+4# is concave up or concave down and its intervals?

##### 1 Answer

Nov 4, 2016

#### Explanation:

To find where a function is concave up, find where the second derivative of the function is positive.

Find

Next, find

Set

After checking the signs of values around these numbers, we find that

graph{-x^4-9x^3+2x+4 [-10, 5, -1000, 1000]}