>>13364620look at the triangle
f is a part of the segment A.
f is equal to the distance between Oc and o.
i know that Zc is really the entire ray Z, which goes off into infinity, but for the sake of explaining im treating it as if Zc terminates at the point where the letter <A> is.
so from Oc (the origin) to Zc, we'll treat is as a segment.
from Oc to o, that's the segment of length f.
and from o to A, that's some other segment.
Zc is the sum of f (or Oc to o), plus (o to A)
the point is that f (Oc to o) is included in the bigger line represented as A (or what we are calling Zc).
(1.) so we have the ratio ratio of Zc / f
now look at the line going from Oc, through p(x,y), to P(Xc, Yc, Zc)
just how <f> is a subset of Zc, so too is x (at point p) a subset of Xc
going from Oc to p(x,y) compared to going from Oc to P(Xc,Yc,Zc); that ratio is the same as going from
Oc to o (aka f) and going from Oc to A (aka Zc)
and yeah, its because they're similar triangles
