$(E,D,F )$ and $(B,A,F)$ are collinear, and $\overline{EC} = \overline{CD} = \overline{BC}$. Also, $CB \bot BA$. The length of $ED$ is $a$, and the length of $DF$ is $b$. Then find the length of $FB$ in terms of $a$ and $b$.

In the above figure, points