Show that
\(
cos\theta.\begin{bmatrix}
cos\theta &sin\theta \\[0.3em]
-sin\theta&cos\theta \\[0.3em]
\end{bmatrix}+sin\theta.\) \(
\begin{bmatrix}
sin\theta & -cos\theta \\[0.3em]
-sin\theta & sin\theta \\[0.3em]
\end{bmatrix}=1\)
cosθ. [(cosθ, sinθ)(-sinθ,cosθ)] + sinθ. [(sinθ,-cosθ)(cosθ, sinθ)] = 1