Like Tasks (A) and (B), this again involves two rotations, but this time through 60˚ and 120˚ rather than 90˚ and 90˚.
The Quicktime movies show some blue dots being rotated and then the resulting green dots being rotated. [The second movie includes a TRACE of the moving points, which might make it easier to discern the centres of rotation.]
The task is again quite challenging. Play the chosen movie several times and PAUSE it at key moments.
The Worksheet shows a still image from each movie, at the moment when the two rotations have been completed.
NOTE: If needed, you can download a free copy of the QuickTime movie player from here: