Sinusoidal current phase angle question

[yy112]

Homework Statement

The sinusoidal current i1(t) has a phase angle of 60 degrees. Furthermore, i2(t) attains its positive peak 0.25ms earlier than the current in i2(t) (i.e i1(t) leads i2(t)). Both currents have a frequency of 500 Hz. Determine the phase angle of i2(t)

Homework Equations

I think we would use this equation: v1(t) = V1cos(wt + theta1)

The Attempt at a Solution

I just can't find a formula in t he book that adds both currents in order to obtain the missing phase angle. Much help is appreciated!

 

[gneill]

You won't need a 'canned' formula for this problem. The first thing to determine is what fraction of a whole wave period does 0.25ms represent? What's the period of the sinusoids?