Answer:
Average rate of change(A(x)) of f(x) over a interval [a,b] is given by:
![A(x) = (f(b)-f(a))/(b-a)](https://img.qammunity.org/2019/formulas/mathematics/college/gkzxe07ffq42gdwj4k8lj2ay8gqkqndbix.png)
Given the function:
![f(x) = 20 \cdot((1)/(4))^x](https://img.qammunity.org/2019/formulas/mathematics/high-school/b9byzexvb22or9a0bkr57r9qp1c7dlwmgb.png)
We have to find the average rate of change from x = 1 to x= 2
At x = 1
then;
![f(x) = 20 \cdot((1)/(4))^1 = 5](https://img.qammunity.org/2019/formulas/mathematics/high-school/8ls6w20heydpv62beuzgwkxnqz8d1nfche.png)
At x = 2
then;
![f(x) = 20 \cdot((1)/(4))^2=20 \cdot (1)/(16) = 1.25](https://img.qammunity.org/2019/formulas/mathematics/high-school/fu19spet8emzxh7uzf26ig6i56l8dk3p0g.png)
Substitute these in above formula we have;
![A(x) = (f(2)-f(1))/(2-1)](https://img.qammunity.org/2019/formulas/mathematics/high-school/1i9nmlxynctnoeiwdi6giwihggadp06t40.png)
⇒
![A(x) = (1.25-5)/(1)=-3.75](https://img.qammunity.org/2019/formulas/mathematics/high-school/9xun0cwkeh7biw1tyb1awc0g29qekqw3tp.png)
therefore, average rate of change of the function f(x) from x = 1 to x = 2 is, -3.75