# Is #f(x)=-x^5+3x^4-9x^3-2x^2-6x# concave or convex at #x=8#?

##### 1 Answer

#### Answer:

#### Explanation:

When looking for the concavity of a function, it's best to find the second derivative,

When

When

The first derivative of this function is:

The second derivative is:

Plug in

Since