Question

A plane flying horizontally at an altitude of 3 mi and a speed of 440 mi/h passes directly over a radar station. find the rate at which the distance from the plane to the station is increasing when it is 4 mi away from the station. (round your answer to the nearest whole number.)

Answer 1

The distance is increasing at a rate that is the speed of the plane multiplied by the cosine of the angle between its flight path and the direct line to the radar station. That cosine is 4/√(3²+4²) = 4/5, so the distance is increasing at
  440 mi/h × 4/5 = 352 mi/h