Arg (2I) = π why shouldn't it be = Arg (2)? The original problem is to find the expansion rate and rotation angle of W = Z ^ 2

Arg (2I) = π why shouldn't it be = Arg (2)? The original problem is to find the expansion rate and rotation angle of W = Z ^ 2

incorrect
2I on the positive half axis of the imaginary axis
So the argument is π / 2