I have a particular question regarding these formulas,

why is their implementation is :

angle_rads[:, 0::2] = np.sin(angle_rads[:, 0::2])

angle_rads[:, 1::2] = np.cos(angle_rads[:, 1::2])

instead of :

angle_rads[:, 0::2] = np.sin(angle_rads[:, 0::2])

angle_rads[:, 1::2] = np.cos(angle_rads[:, **0::2**])

what is inside the sin and cos parentheses is similar.