Question

Square OABC is drawn on a centimetre grid. O is (0,0) A is (2,0) B is (2,2) C is (0,2) Write down how many invariant points there are on the perimeter of the square when OABC is rotated 90 degrees clockwise, centre (2,0).

Answer 1

There is one point: A (x, y) = (2, 0)

Explanation:

A point of the square OABC is invariant only if its location coincides with location of the rotation axis, that is, that such point experiments only rotation, no translation in any form. The center of rotation coincides with the location of one of the vertices of the square and, therefore, there is one invariant point on the perimeter: A (x, y) = (2, 0)