Let $\triangle ABC$ be a right triangle such that $B$ is a right angle. A circle with diameter of $BC$ meets side $AC% at $D$ If $AD = 1$ and
$BD = 4,$
then what is
BDC is an inscribed angle in the circle with endpoints at the diameter. That means BDC is 180/2 - 90 degrees.
Knowing that, can you use similar triangles to figure out CD?