<s>[INST] A triangle $ABC$ has side lengths $AB = 30$, $BC = 20$, and $AC = x$. The triangle is situated in a circle, and $AD$ is the altitude from vertex $A$ to side $BC$. The length of $AD$ is 15. Since triangles $ABD$ and $ACD$ are right triangles, use the Pythagorean Theorem to find the value of x.[/INST]