# Math Help - Signals and Systems: Determine if the signal is periodic or nonperiodic(show solution

1. ## Signals and Systems: Determine if the signal is periodic or nonperiodic(show solution

Determine whether or not each of the following signals is periodic if signal is periodic determine the fundamental period (note that these are discrete not continuous signals)
1. $x(n) = \cos^3(\frac{\pi(n)}{8})$

2. $x(n) = \cos(\frac{n}{2})\cos(\frac{\pi(n)}{4})$

do i need to do trigonometric identities ? I read in the book that the sum of two periodic signals is "periodic" and it does not mention "product" where the given equation above is the case

An easy example to guide the helpers is this
x(n) = cos(2n)
f = w/(2pi) = 2/(2pi) = 1/pi ----> this is an irrational number hence it is not periodic

2. This Wikipedia Article defines a periodic function: Periodic function - Wikipedia, the free encyclopedia

Once you understand what a periodic function is, take a look at both of the given functions:

http://www.wolframalpha.com/input/?i=y%3Dcos^3((pi*x)/8)

http://www.wolframalpha.com/input/?i=y%3Dcos(x/2)cos((pi*x)/4)