circuit analysis question

[ocmyface]

im in circuit analysis, and we're studying AC steady-state analysis and all the phase BS that accompanies it.

i'm trying to read through my book and figure this out since i missed class but the book isn't too useful.

the question is this:

given i(t) = 5 sin (377t - 20(degrees))
and v(t) = 10 cos (377t + 30(degrees))

determine the phase relationship...

according to the book, before i can determine the relationship three things must be true:

1) frequency of both sinusoids must be the same
2) amplitude of both sinusoids must be positive
3) both sinusoids must be written as sin or cos functions

looking at the problem, 1 & 2 are true. but does 3 mean both must be sin/cos or can one be sin and one be cos?

if both must be sin or cos. than i can just convert the cos to sin by adding 90 degrees to the phase angle, correct?

so than it would be (for v) (30 dgres + 90 dgres) = 120 so -20 (i(t)) - 120 = -140 so i(t) lags v(t) by 140 degrees?

thanks for the help

[xlink]

I'd say that 3 simply means that only trignometric functions are allowed.

namely y=x * cos(x) is not allowed, but y = 3 * cox(x)