GATE Chemical 2018 | Question: 47

Question

For the matrix $A=\begin{bmatrix} \cos\theta &-\sin\theta \\ \sin \theta & \cos\theta \end{bmatrix}$ if $\det$ stands for the determinant and $A^{T}$ is the transpose of $A$ then the value of $\det(A^{T}\:A)$ is _____________