2-Proportion & Theorem

<p>A 2-Proportion is an expression a:b where a, b ∈ Rational Numbers (Rat), not both 0, with the convention that:

<i>a:b =&#160;λa:λb for any </i>λ≠0

&#160;

Theorem:

a:b = c:d ⇔ ad-bc = 0</p>