Itâs a cost-benefit analysis: If it costs you 3 hours weekly to do the wash, but costs you $30 to send it out â that is $10 per hour. But if you bill more than that at your business â or stand to get a raise if you use those three hours to learn new skills, earn a degree, etc., it is worth the investment.
Coordinate Rules for Rotations. In general, we can state the following coordinate rules for (counterclockwise) rotations about the origin: For a rotation of 90o: (x, y) --> (ây, x) For a rotation of 180o: (x, y) --> (âx, ây) For a rotation of 270o: (x, y) --> (y, âx)
A rotation takes the form of a special orthogonal matrix, where special is a technical term meaning the determinant is +1. The determinant of any orthogonal matrix is either +1 or â1, so fully half of them do not correspond to rotations. For example, in the description of point groups for crystallography we have not only rotations, but also reflections, inversions, and rotary reflections.