Radian : The angle made by taking the radius and wrapping it along the edge of the circle.
One Radian is 180/π degrees, or about 57.296°
Radical: The root of a quantity as indicated by the radical sign.
Radius: A line segment drawn from the center of a circle to a point on the circle.
Random : Without order. Not able to be predicted. Happening by chance.
Range (statistics): The difference between the lowest and highest values.
Range of a function : The set of all output values of a function.
Rate : Rate = distance traveled / time taken. Its unit is either m/s or km/h.
Ratio : A ratio shows the relative sizes of two or more values. Ratios can be shown in different ways. Using the ":" to separate example values, or as a single number by dividing one value by the total.
Rational Expression : An expression that is the ratio of two polynomials.
Rational Number : Any number that can be made by dividing one integer by another. The word comes from "ratio".
Ray: Given any two points A and B , AB is equal to the union of AB and all of those points.
Real Number : Positive or negative, large or small, whole numbers or decimal numbers are all Real Numbers.
Reason: A true statement justifying a step in a proof; the use of logic, examples, etc. to determine a result.
Rectangle: A parallelogram containing one right angle; a quadrilateral with four right angles.(from math dictionary r)
Rectangular coordinates: An ordered pair of real numbers that establishes the location of a point in a coordinate plane using the distances from two perpendicular intersecting lines called the coordinate axes. (See also Cartesian coordinates.)
Rectangular Prism (Cuboid) : A solid (3-dimensional) object which has six faces that are rectangles.
Recurring Decimal : A decimal number that has digits that repeat forever.
Reflection: An isometry where if l is any line and P is any point not on l , then rl (P) = P' where l is the perpendicular bisector of PP' and if P∈l then rl(P) = P .
Reflexive property of equality: A property of real numbers that states a = a .
Reflex angle : A Reflex Angle is more than 180° but less than 360°
Regular polygon : A polygon which is both equilateral and equiangular.
Regular pyramid: A pyramid whose base is a regular polygon and whose lateral faces are congruent isosceles triangles.
Remote interior angles: Either interior angle of a triangle that is not adjacent to a given exterior angle of the triangle. Also called non-adjacent interior angles.
Restricted domain: The domain resulting from a restriction placed on a function, based on the context of the problem.
Rhombus: A parallelogram with two adjacent congruent sides; a quadrilateral with four congruent sides.
Right angle: An angle formed by two perpendicular lines, the measure of which is 90°.
Right circular cylinder: A cylinder whose bases are circles and whose altitude passes through the center of both bases.
Right Angle : A right angle is an angle which is equal to 90°, one quarter of a full revolution.
Right circular cone: A cone whose base is a circle and whose altitude passes through the center of its base.
Right pyramid: A pyramid whose lateral faces are isosceles triangles.
Right triangle: A triangle with one right angle.
Roman Numerals :How ancient Romans used to write numbers. I, V, X, L, C, D, M are the symbols used.
Root : Where a function equals zero.
Rotation: An isometry where if P is a fixed point in the plane, θ is any angle and A ≠ P then ' Rp,θ(A) = A' where m∠APA' =θ and Rp,θ(P) = P
Rotational symmetry: A geometric figure has rotational symmetry if the figure is the image of itself under a rotation about a point through any angle whose measure is not a multiple of 3600.A regular hexagon has rotational symmetry of 600 , 1200 , 1800 , 2400 , and 3000 (from math dictionary r)
Run : How far a line goes along (for a given distance going up). Rise/Run gives you the slope of the line. Math dictionary r