If \( A = \begin{bmatrix} \sin \theta & \cos \theta \\ -\cos \theta & \sin \theta \end{bmatrix} \) and \( A + A' = I \), then \( \theta \) is equal to :
Show Hint
When adding a matrix to its transpose, the diagonal elements always double (\( 2a_{ii} \)), while the off-diagonal elements become \( a_{ij} + a_{ji} \). If the matrix is skew-symmetric, the off-diagonal sum cancels out completely to zero.