Question

A spectator watches a helicopter which flies at a constant altitude of 80m at a speed of 10m/s. At what rate is the angle of elevation from the feet of the spectator to the helicopter (see figure) changing 6 seconds after the helicopter passes directly above the spectator.

Answer 1

first step is to draw a picture of what is going on

Answer 2

we are given dx/dt=10m/s
where x is the distance the helicopter has flew
let's call the angle of elevation theta