Understanding Why C/d = pi is a Constant

[Hepic]

Lets say that "d" is diametr of a circly,and C is the perimetr(length).
Why C/d = pi (3.14) is a constant?? I know the proof of archimides with poligons,from which found the value of pi,but how we know that C/d is always equal with a constant that we named as π=3.14;

Thanks !

 

[Hepic]

I found it guys. The proof use similar triangles etc...
Thanks for your time !

 

[thelema418]

I found it guys. The proof use similar triangles etc...
Thanks for your time !

This also requires assumptions of Euclidean geometry. In spherical geometry it is not constant.