One more Vector problem and we are good to go!!! The Problem: Find the change in velocity of a yacht if it changes its velocity from 5ms^-1 due north to 3ms^-1 due west and also state its direction. The solution : (resultant vel.)^2 = 5^2 + 3^2 = 5.8 ms^-1 direction = tan-1(3/5) = 31 degrees west of north However , the books answer is 5.8 ms^-1 in a direction 31 degrees west of south . what am i doing wrong here ???