Question

What is the Basic form of the triangle wave function??

Answer 1

I'm not sure what you mean by "basic" but whenever I write generalized triangle wave equations I use the following form:
\[y(x)=\frac{2A}{\pi}\sin^{-1}[\sin(\frac{2\pi}{T}x)]\]
Here A is the amplitude of the wave, and T is the period.

Answer 2

I also know triangle waves can be written as piecewise functions, but I don't know if you consider that more basic.