Find the matrix

Algebra Level 3

\[P= \begin{bmatrix} \cos\cfrac { \pi }{ 4 } & -\sin\cfrac { \pi }{ 4 } \\ \sin\cfrac { \pi }{ 4 } & \cos\cfrac { \pi }{ 4 } \end{bmatrix} \qquad \qquad X = \left[ \begin{matrix} \cfrac { 1 }{ \sqrt { 2 } } \\ \cfrac { 1 }{ \sqrt { 2 } } \end{matrix} \right] \]

For matrices \(P\) and \(X\) as defined above, find \(P^3X\).