How do I find the phase difference between two oscillators

[Fysicsfailure]

Homework Statement

Find the phase difference between two harmonic oscillators at time t=1

Homework Equations

I've already found x(t)= .4 cos(2.1t) and x(t)= .4cos((pi/2)t + pi)

The Attempt at a Solution

I don't really know where to begin

 

[TSny]

Hello, and welcome to PF!

Start with recalling (or finding) the definition of the word "phase" for simple harmonic motion.

 

[Fysicsfailure]

Hey thanks! :)

Oh wow...Okay now I got it. Just plug in 1 for t and subtract the two terms in the parentheses. Thanks for the lead!