Calculate the phase angle between two sinusoids

[DryRun]

Homework Statement

Calculate the phase angle between two sinusoids.

Relevant Equations

v1(t) = -10cos(wt + 50) and v2(t) = 12sin(wt-10)

I am trying to do exactly what was stated, by finding it with calculations only, so, without having to draw the curves. Is that possible?

Here is my attempt:

v1(t) = -10cos(wt + 50) and v2(t) = 12sin(wt-10)
v1(t) = -10cos(wt + 50) becomes v1(t) = -10sin(wt+50+90) = v1(t) = -10sin(wt+140)

Now, i have these equations: v1(t) = -10sin(wt+140) and v2(t) = 12sin(wt-10).
If there was no negative sign in front of the 10, then i could have simply found the phase angle by: 140--10 = 150 degrees, but since it has a negative sign, I'm not sure what to do.

 

[scottdave]

What is the phase difference of (multiplying by negative)? Think of a vector pointing in a direction. Now think of the "negative" of that vector. What's the angle between those vectors?

 

[scottdave]

Did you figure it out @DryRun ?