Question

would a straight line be considered to be periodic function?

Answer 1

A periodic function is a function that has some form repetition that can be mathematically described. Most of the the time high school or undergraduates see periodic functions is when dealing with trigonometric equations. This includes equations in the form of:
\[y = \cos x\]
\[y = \sin x\]... etc, because they repeat despite the size of x! Therefore they are periodic functions. Even y = tan x could be considered periodic, even though it's not continuous.

Answer 2

would a straight line be periodic, even though it goes at a constant rate?

Answer 3

no

Answer 4

a function is periodic with period \(p\) if \(p\) is the smallest number for which \(f(x)=f(x+p)\) for all \(x\)