Let A= (cos α, - sin α; sin α, cos α),(α ∈ R ) such that A^32= (0, -1; 1, 0). Then a value of α is:

Let $\displaystyle A=\left(\begin{array}{cc}\cos \alpha & -\sin \alpha \\ \sin \alpha & \cos \alpha\end{array}\right),(\alpha \in \mathbf{R})$ such that $\displaystyle \mathrm{A}^{32}=\left(\begin{array}{cc}0 & -1 \\ 1 & 0\end{array}\right)$. Then a value of $\displaystyle \alpha$ is :