Need a step by step on finding the average rate of change for $x^3-2x+8$

I am trying to solve a rate of change problem. The answer is given but I do not understand where the math comes from. I am new to this subject in algebra. It is asking for the average rate of change from -4 to -3 for the equation $x^3-2x+8$?

How is this 35/1? I used the equation $\frac{f(x_2)-f(x_1)}{x_2-x_1}$ but I am not getting the 35/1.

• You are presumably having minus sign trouble. $f(-3)=-13$ and $f(-4)=-48$, So it is $35$. – André Nicolas Oct 31 '14 at 0:33

In this question, $x_2 = -3$ and $x_1 = -4$, try plugging these numbers in and be careful with negative signs. Remember that $x_2$ is second input value (thus the $2$), and $x_1$ is the first.