Apologies if this is better suited for a mathematics forum, it's from my circuits textbook so I've decided to post here. Below is a practice problem from the textbook, with the provided solution.
If I try to convert i1 to a positive cosine function, I get 4cos(377t+140) by shifting -90 (converting to cos) and then shifting +180 (negating the amplitude). So I am then comparing i1=4cos(377t+140) and i2=5cos(377t-65), so a 205 degree phase angle between the functions, where 210 is the stated answer. Is this a mistake in the textbook? I spend hundreds for textbooks and I've spent more time verifying errors than reading... :( oh well
Additionally, it seems to me which function leads which is rather relative as I can shift any function 360 deg, any easy reconciliation?