You know the period of the cos function is <span>2π</span>, right? Every <span>2π</span> that the argument to cos goes through is one complete cycle. You've multiplied the argument by <span><span>2π</span>3</span> so that changes the period. If we had simply multiplied by 2, you would have 2 cycles per <span>2π</span> change in θ instead of the usual 1, and the period would be correspondingly halved. Can you figure out the new period in your equation?
The amplitude is easy to find. The value of cos<span> varies from 1 to -1. You've multiplied it by 1/4. What will that do to the amplitude?</span>
