## concave
concavus for "hollow." A biconcave
lens has two concave surfaces, not necessarily with the same radii
of curvature. A figure, such as a polygon or polyhedron, is said to be concave
if a line segment joining any points inside the figure goes outside the
figure. Similarly, a set is concave if it doesn't
contain all the line segments connecting any pair of its points. Compare
with convex. ## Related categories• OPTICS AND OPTICAL PHENOMENA• MATHEMATICAL TERMINOLOGY | |||||||

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