R: abbreviation for the real numbers.

radian: the ratio of an arc of a circle to the radius of the circle. On a unit circle, a full

rotation around the circle is 2pi radians. On any circle, a full rotation is 2pi r

radians.

radius: the distance from the center to a point on a circle. The line segment from the

center to a point on a circle.

range: the set of all possible values for the output of a function.

ratio: the ratio of two real numbers, a and b, is a/b.

rational number: a number that can be expressed as the ratio of two integers.

real numbers: the union of the set of rational numbers and irrational numbers.

reciprocal: the reciprocal of a number, a, is 1/a, (a cannot be zero).

rectangle: a quadrilateral with four 90 degree angles.

rectangular coordinates: same as Cartesian Coordinates.

reflection: mirror image.

reflexive property: x = x for all x. Every number equals itself.

regular polygon: a polygon in which all the angles are equal and all of the sides are equal.

regular polyhedron: a polyhedron whose faces are congruent, regular polygons.

relation: a set of ordered pairs.

remainder: if m = nq + r, then m/q has quotient q and remainder r.

repeating decimal: a decimal in which the digits endlessly repeat a pattern.

rhombus: a quadrilateral with four equal sides.

right angle: an angle whose measure is 90 degrees.

right circular cone: a cone whose base is a circle located so that the line connecting the

vertex to the center of the circle is perpendicular to the plane

containing the circle.

right circular cylinder: a cylinder whose bases are circles and whose axis is perpendicular

to its bases.

right triangle: a triangle that contains a right angle.

root: the root of an equation is the same as the solution to the equation.