15) Period of y = cos 3x

One way is probably to generate a graph.

y=cos(3x)

The cosine function has a period of 2\pi. If you multiply "x" by 3, the function will repeat (cycle) three times as x goes from 0 to 2\pi. Therefore, the period is \frac {2 \pi}{3}.

Here's a link to help you visualize it.

Cosine Function (http://www.analyzemath.com/cosine/cosine.html)

Click on the "Click here to start" button and move the sliders.

The amplitude is the same as the normal cosine function (range -1 to +1). If you wished to change that, you'd have to multiply the cosine function by something.

Ok, just remember that in a given function y = a cos (bx) +c or y = a sin (bx) + c,

The amplitude will be given by a,

The period will be given by \frac{360}{b} or \frac{2\pi}{b}