## Calculus: Early Transcendentals (2nd Edition)

$d$=dependent variable $t$=independent variable Domain: [0,2]
Since the distance depends on the time elapsed, distance $d$ is the dependent variable and time $t$ is the independent variable. The domain consists of the appropriate values of $t$. The time begins with $t=0$ and ends when the stone hits the river. We can find this time by setting $d=0$: $20-5t^2=5(4-t^2)=5(2-t)(2+t)=0$ $t=2$, $t=-2$ We ignore $t=-2$, since this solution goes backwards in time. Thus the domain is [0,2]