Difference between phase angles

[kostoglotov]

Homework Statement

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imgur: http://i.imgur.com/9ktFGSs.png

Homework Equations

The Attempt at a Solution

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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?

 

[Charles Link]

Is it 210 ahead or 150 behind? Both are correct. If they are 180 degrees apart, does it lead by 180 or lag by 180 ? It is impossible to make such a distinction. Both answers are correct.