Should you find theta?

\[\large x_n=2^n \cos n\theta\]

For the given sequence we know that \(\large x_2=-\frac{28}{9}\) and \(\large x_3=- \frac{184}{27}.\)

If \(x_4=\dfrac{A}{B},\) where \(A\) and \(B\) are coprime positive integers, find \(A+B.\)

SeePart 2.