1. The problem statement, all variables and given/known data imgur: http://i.imgur.com/9ktFGSs.png 2. Relevant equations 3. The attempt at a solution I came up with both 150 and 210 as the difference between the phase angles. I chose 150. If you draw the vectors and compare their angles, the angular difference between them could be either 150 or 210. Can you choose either? If not, why did the text choose 210?