Brian is in a lighthouse 3 miles from the nearest point O of a straight shoreline. Brian would like to visit his friend Torre who lives 5 miles up the beach from the point O. Brian can row 3 miles per hour and run 8 miles per hour. In order to get to Torres house in the least amount of time, to what point on the beach should Brian row and leave his boat?
If he heads for a point x miles from O, then the time needed is
t = √(x^2+9)/3 + (5-x)/8
dt/dx = 0 when x = 9/√55