In the isosceles triangle \(ABC\), \(AB = AC\) and \(\angle A = 100^\circ\). Point \(D\) is a point on \(AB\) such that the line \(CD\) bisects \(\angle ACB\). Given that \(CD = 55\) and \(AD = 18\), the length of \(BC\) can be expressed in the form \(x^2 + y^2\). What is the value of \((x + y)^2\)?