1.
Let n2n\ge2 be integer. A=[cos(2π/n)sin(2π/n)0sin(2π/n)cos(2π/n)0001]A = \begin{bmatrix}\cos(2\pi/n)&\sin(2\pi/n)&0\\-\sin(2\pi/n)&\cos(2\pi/n)&0\\0&0&1\end{bmatrix} and II identity. Then