Mediant is Between/Corollary 2

Corollary to Mediant is Between
Let $a, b, c, d \in \R$ be real numbers such that $b > 0, d > 0$.

Let $\dfrac a b = \dfrac c d$.

Then:
 * $\dfrac a b = \dfrac {a + c} {b + d} = \dfrac c d$