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


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.