While this problem looks straight from a differential calculus textbook, it requires no advanced math.
Two bugs sit on either side of a bubble. The radius r of the bubble is expanding with dr/dt=3 cm/s. The distance between the bugs is d and they sit on either side of a 60 degree arc, find dd/dt when r=2.
Since the arc is 60 degrees, then d=r and thus dd/dt=dr/dt, dd/dt=2 at all times.
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