(4) - Outcoming

$\text{DE}$ is the bisector of $\widehat{\text{CDB}}$ ( $\text{E} \in \text{BC}$ ). $\text{ABCD}$ is a quadrilateral that $\widehat{\text{BCD}} = \widehat{\text{CDA}}$ and $\widehat{\text{EDA}} = \widehat{\text{DAB}} = 90^\circ$ . If $\text{DB} = 6\sqrt 5$ ; $\text{CD} = 2\sqrt{\dfrac{3}{5}}$ and $\text{EA} = 2\sqrt{13}$ , then $\text{CD} = \sqrt{\dfrac{a}{b}}$ , with $(a, b) = 1$ . Calculate the value of $ab$ .