Glossary of Geometry Terms
area—the two-dimensional surface included within a set of lines
axis—a straight line that divides a shape symmetrically
circumference—the outer boundary of a circle
constant—a number that in a given mathematical situation doesn’t change
equilateral—having all sides of equal length
irrational number—a number that can’t be derived from dividing one ordinary whole number into another, and whose decimal continues without end and without repeating sequences
polygon—a two-dimensional shape that’s closed (no gaps between lines) and made of straight lines; a regular polygon is a polygon with all sides of the same length and all angles of equal size
radius—a straight line from the center of a circle to its circumference, or from the center of a regular polygon to any of its vertices
ratio—the size relationship between two numbers
square root—to get the square of a number, multiply it by itself (3 squared = 3 x 3 = 9); the square root of a number is the value that, when squared, gives you that number (the square root of 9 = 3)
subset—a smaller group within a larger group: for example, transcendental numbers are a subset of irrational numbers (all transcendental numbers are irrational numbers, but not all irrational numbers are transcendental numbers)
transcendental number—a special class of irrational numbers that defy easy mathematical description
vertex (plural vertices)—the point at which two straight lines meet
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