| 释义 |
symmetrical about a point A plane figure is symmetrical about the point O if, whenever P is a point of the figure, so too is P′, where O is the midpoint of P′P. The point O is called a centre of symmetry; and the figure is said to have rotational symmetry of order 2 about O because the figure appears the same when rotated through half a revolution about O. The graph of an odd function is symmetrical about the origin.
|