Answer
$f(x)=500(0.5)^{x}$
Work Step by Step
When $x$ increases by $1,\quad f(x)$ is halved
(multiplied by $0.5.$)
$\Rightarrow b=0.5$
$f(0)=500$
$Ab^{0}=500\Rightarrow \quad A=500$
Thus,
$f(x)=500(0.5)^{x}$
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