The above function is to be used if the value of x is between 0 and 8. On the other hand, the function to be used when x ≥ 8 is -5x + 11.
Since the interval to be checked is from 2 to 7, we will be using the first function which is -2x + 4.
To determine the rate of change between those intervals, we have the formula below:
[tex]\text{rate of change = }\frac{f(x_2)-f(x_1)}{x_2-x_1}[/tex]Let's solve f(x₂) first. Our x₂ = 7. Let's substitute the function above with x = 7.
[tex]\begin{gathered} f(x)=-2x+4 \\ f(7)=-2(7)+4 \\ f(7)=-14+4 \\ f(7)=-10 \end{gathered}[/tex]Let's solve f(x₁) first. Our x₁ = 2. Let's substitute the function above with x = 2.
[tex]\begin{gathered} f(x)=-2x+4 \\ f(2)=-2(2)+4 \\ f(2)=-4+4 \\ f(2)=0 \end{gathered}[/tex]So, we now have the value of f(x₂) = -10, and f(x₁) = 0. Let's use these values to the formula of the rate of change above.
[tex]\begin{gathered} \text{rate of change}=\frac{f(x_2)-f(x_1)^{}}{x_2-x_1} \\ \text{rate of change}=\frac{-10-0}{7-2} \\ \text{rate of change}=\frac{-10}{5} \\ \text{rate of change}=-2 \end{gathered}[/tex]Since the rate of change is a negative number, the function is decreasing over the interval [2, 7].