1. Show, from the definition, that if A:B::C:D and C:D::E:F then A : B :: E : F.
writing the ratios as fractions, you have
a/b = c/d
and
c/d = e/f
So, transitivity means that
a/b = c/d = e/f
a/b = e/f
a/b = c/d
and
c/d = e/f
So, transitivity means that
a/b = c/d = e/f
a/b = e/f