Prove that the determinant `|(x,sin theta,cos theta),(-sin theta,-x,1),(cos theta,1,x)|` is independent of `theta`

Explanation

To prove that the determinant

\[
D = \begin{vmatrix}
x & \sin \theta & \cos \theta \\
-\sin \theta & -x & 1 \\
\cos \theta & 1 & x
\end{vmatrix}
...