| 释义 |
symmetrical about a line A plane figure is symmetrical about the line l if, whenever P is a point of the figure, so too is P′, where P′ is the mirror-image of P in the line l. The line l is called a line of symmetry; and the figure is said to have bilateral symmetry and is invariant under reflection in the line l. The graph of an even function is symmetrical about the y-axis.
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