Find the Exact Value arccos(sin((5pi)/2))

Subtract full rotations of ${\displaystyle 2\pi }$ until the angle is greater than or equal to ${\displaystyle 0}$ and less than ${\displaystyle 2\pi }$.

The exact value of ${\displaystyle \sin \left(\frac{\pi }{2}\right)}$ is ${\displaystyle 1}$.