RECTANGLED

, Right-angled, or RECTANGULAR, is applied to figures and solids that have at least one right angle, if not more. So a Right-angled triangle, has one right angle: a Right-angled parallelogram is a rectangle, and has four right angles. Such also are squares, cubes, parallelopipedons.

Solids are also said to be Rectangular with respect to their situation, viz, when their axis is perpendicular to their base; as right cones, pyramids, cylinders, &c.

The Ancients used the phrase Rectangular section of a cone, to denote a parabola; that conic section, before Apollonius, being only considered in a cone having its vertex a right-angle. And hence it was, that Archimedes entitled his book of the quadrature of the parabola, by the name of Rectanguli Coni Sectio.