How fast is the plane traveling at that time? A plane flies horizontally at an altitude of 6 km and passes directly over a tracking telescope on the ground. When the angle of elevation is pi/4 , this angle is decreasing at a rate of pi/4 rad/min. __________________km/min.
Let x be the horizontal (ground) distance from the tower and `theta` the angle of elevation from the tower to the plane.
Then `tan theta=6/x` . Taking the derivative with respect to t we get:
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