



 
Hi Steven, I drew a diagram of the situation $t$ hours after the plane was directly over the car. $P$ is the position of the plane, $C$ is the position of the car, $G$ is the point on the ground directly below the plane and $O$ is the point on the ground where the car was when the plane was overhead. The measure of the angle $GOC$ is $\large \frac{\pi}{4}$ radians. All the distances are in miles. You are to find $s^{\prime}(t)$ when $t = 36$ seconds. Since triangle $PCG$ is a right triangle, if you can find $g(t)$ you can use Pythagoras theorem to obtain an expression for $s(t)$ which you can then differentiate and evaluate at $t = 36$ seconds. Make sure you convert $36$ seconds to hours first. How do you determine $g(t)?$ I would use the Law of Cosines. Penny  


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