GEOMETRIC SHAPES

There are numerous geometric shapes used in mathematics. The most common are listed below.

circle A continuous line or the plane bounded by such a line, in which every point of the line is equidistant from the central point lying on the plane. A circle is commonly described by its radius-a straight line extending from the center of the circle to any point on the perimeter-and its diameter-a straight line extending from a point on the perimeter, through the center, to a point on the perimeter on the other side of the circle (it is also expressed as twice the radius).

square A four-sided figure that has four lines at 90° angles. The opposite sides are parallel to each other and all sides are of equal length.

triangle A three-sided figure that can take several shapes. In general, it has three inside angles, which add up to 180°. Triangles are divided into three basic types: obtuse, right, and acute; triangles named by the characteristics of their sides are equilateral, isosceles, and scalene.

polygon A geometric figure that is bound by many straight lines (see also "Names for Polygons," later this chapter).

rectangle A four-sided figure that has four lines at 90° angles. The opposite sides are parallel to each other and are equal in length, but are not equal in length to the lines that run perpendicular to them.

cube A solid that has six square sides, with each at right angles to each adjacent side. cylinder A solid that has two equal-sided circular bases and a third side that joins the bases.

sphere A solid that is bounded by a curved surface. Any point measured from the outside of the sphere to the center of the sphere is equal in distance.

rectangular prism A solid that has four sides, with each junction at 90° angles. The opposite sides are equal in length and parallel to each other, but they are not equal in length to the sides that run perpendicular to them.

from:  The New York Public Library Science Desk Reference (Macmillan, 1995)