Answer:
![f(x)=20,000(0.85)^x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/p1wruasvtkvbyecswz9s7enbdkok9mqsv2.png)
Explanation:
We know that the exponential decay (depreciation) equation with rate of decay r in time period x is given by :-
, A is the initial value .
Given: The initial value of truck = $20,000
Rate of depreciation= 15% = 0.15
Now, the function represents the car's value after x years is given by ;-
![f(x)=20,000(1-0.15)^x\\\\\Rightarrow\ f(x)=20,000(0.85)^x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/s5so0jyfpnxvozsvdou2ydtslct0k33g8y.png)