A missile is fired at an airplane and is always directed toward the airplane. The missile is traveling at twice the speed of the airplane. An equation that describes the distance r between the missile and the airplane is

where θ is the angle between their directions at all times. See Fig. 21.119. This is a relative pursuit curve. Sketch the graph of this equation for π/4 ≤  π ≤ π.

r = 70 sin0 (1 - cos 0)