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trignometric differentiation

An aircraft climbing at a constant angle of 30

above the horizontal passes directly over a ground radar station at an altitude of 1 km. At a later instant, the radar shows that the aircraft is at an air distance of 2 km from the station, and that this distance is increasing at 7 km/min. What is the speed of the aircraft at that instant? [Note: the law of cosines may be useful.] At what rate is the angle between the vertical line directly above the station and the line from the station to the aircraft changing?

--->I found the angle to be 34. To find the velocity at that point do I need to first find the distance and then differentiate the cosine law? Also, please guide me through the rate of change of angle.