a ship A is 5 nautical miles due north of ship B. Ship A is steaming due west of at 15 knots and B is steaming due north west at 10 knots. Find the distance and the time of their nearest approach to each other
After t hours, the distance d can be found by
d^2 = 15t^2 + (5-10t)^2
2d dd/dt = 30t + 2(5-10t)(-10)
2d dd/dt = 230t-100
dd/dt = (230t-100)/(2d)
since d is never zero, that means
dd/dt=0 when t = 10/23 hours