Inscribed circle.

In a right triangle $ABC$ , right angled at $C$ , $AB=c$ , $AC=\dfrac{3}{5}c$ .A circle with center $O$ is inscribed in the triangle .Let $OC$ intersect the circle at point $D$ . $CD$ can be expressed in function of $c$ , $CD=f(c)$ .If $f(c)=\dfrac{c}{5}*(\sqrt{x}-1)$ .Find $x$ .