Refer to the figure: In right triangle $ABC$ with right angle at $C$, the base $AC$ is divided into segments of lengths $a$ and $b$ by a perpendicular from a point on $AB$ to $AC$. This perpendicular has length $x$, and the vertical leg $BC$ has length $y$. If the area of triangle $ABC$ is $A$, which of the following expresses $x$ in terms of $A$, $a$, and $b$?