Given:
The function is
[tex]f(x)=-x^2-5x+12[/tex]
To find:
The average rate of change of the function over the interval −5 ≤ x ≤ 4.
Solution:
The average rate of change of a function f(x) over the interval [a,b] is
[tex]m=\dfrac{f(b)-f(a)}{b-a}[/tex]
Putting x=-5 in the given function, we get
[tex]f(-5)=-(-5)^2-5(-5)+12[/tex]
[tex]f(-5)=-25+25+12[/tex]
[tex]f(-5)=12[/tex]
Putting x=4 in the given function, we get
[tex]f(4)=-(4)^2-5(4)+12[/tex]
[tex]f(4)=-16-20+12[/tex]
[tex]f(4)=-24[/tex]
Now, the average rate of change of the function over the interval −5 ≤ x ≤ 4 is
[tex]m=\dfrac{f(4)-f(-5)}{4-(-5)}[/tex]
[tex]m=\dfrac{-24-12}{4+5}[/tex]
[tex]m=\dfrac{-36}{9}[/tex]
[tex]m=-4[/tex]
Therefore, the average rate of change of the function over the interval −5 ≤ x ≤ 4 is -4.
