# Math Dictionary r

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**R**

**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 r

_{l}(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 ' R

_{p,θ}(A) = A' where m∠APA' =θ and R

_{p,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 360

^{0}.A regular hexagon has rotational symmetry of 60

^{0}, 120

^{0}, 180

^{0}, 240

^{0}, and 300

^{0}(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**

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