Chapter 2 - Review - Modeling with Functions - Problems - Page 241: 13

$D(t)=25t$

First, one must find the distances of each ship based on time, $t$ $d_{1}=15 t$ $d_{2}=25 t$ Now, since the ships parted ways in a right angle, one can use the Pythagorean theorem to find $D$, which is the hypotenuse: $D^2=(d_{1})^2+(d_{2})^2$ $D=\sqrt{(d_{1})^2+(d_{2})^2}$ $D=\sqrt{(15t)^2+(20t)^2}$ $D=\sqrt{225t^2+400t^2}$ $D=\sqrt{625t^2}$ $D(t)=25t$