Radius, Ratio, Ray

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Our Math Dictionary words that start with R has the Math terms that start with the letter R. Start here with Math definitions that we have gathered from a half dozen Math books, including a very old one.

**Radian** - a special unit of measure that measures things that are circular.

**Radical** - a root of a number.

**Radical Axis** - the locus of points of equal power with respect to two circles.

**Radical Center** - the radical center of three circles is the common point of intersection of the radical axes of each pair of circles.

**Radicand** - the number inside the radical sign.

**Radii** - plural of radius.

**Radius** - the length of a straight line drown from the center of a circle to a point on its circumference.

**Radius of a Circle** - a line segment starting at the center and going to the outer edge of the circle. The radius is half of the diameter.

**Radix Point** - the generalization of decimal point to bases of numeration other than base 10.

**Random Number Generators** - a device used to produce a selection of numbers in a fair manner, in no particular order and with no favor being given to any numbers.

**Range** - the range of a set of numbers is the largest value in the set minus the smallest value in the set. Note that the range is a single number, not many numbers.

**Range of the Function F** - the set of all the numbers f(x) for x in the domain of f.

**Rate** - a certain percent of the principal which indicates the interest on one dollar for one year; the number denoting how many hundredths of the base are to be taken.

**Ratio** - a rational number of the form a/b where a is called the numerator and b is called the denominator, a comparison of numbers, the quotient or result of one quantity divided by another (fraction).

**Rational Number** - a number that can be written as a fraction with integers as the numerator and denominator.

**Rationalize the Denominator** - a process that gets rid of the radical in the denominator.

**Ray** - a straight line that begins at a point and continues outward in one direction.

**Real Axis** - the x-axis of an Argand diagram.

**Real Numbers** - consist of both the rational and irrational numbers.

**Real Part** - the real number x is called the real part of the complex number x+iy where x and y are real and i=sqrt(-1).

**Real Variable** - a variable whose value ranges over the real numbers.

**Reciprocal of a Number** - the number need to multiply to get 1 as the answer.

**Rectangle** - a parallelogram with four right angles and four sides.

**Rectangular Coordinate System** - a plane made up of an x axis (the horizontal line) and a y axis (the vertical line).

**Rectangular Solid** - a volume bounded by rectangle faces.

**Recursion** - given some starting information and a rule for how to use it to get new information, the rule is then repeated using the new information.

**Reduce** - to rewrite a fraction in lowest terms.

**Reflect** - to repeat an image by flipping it across a line so it appears as it would in a mirror.

**Reflex Angle** - an angle between 180º and 360º.

**Regrouping** - to rearrange quantities in place values of numbers during calculations.

**Regular Polygon** - a polygon whose side lengths are all the same and whose interior angle measures are all the same.

**Relation** - ordered pair in the form: (x, y)

**Relative Frequency** - the number of items of a certain type divided by the number of all the numbers being considered.

**Relatively Prime** - two numbers that have no common factors other than the number 1.

**Remainder** - amount left that is left after division.

**Remainder** - the dividend remaining when the quotient is not equally divisible by the divisor, also the name of the answer in a subtraction.

**Repdigit** - an integer all of whose digits are the same, 11, 222, 333.

**Repeating Decimal** - a decimal whose digits eventually repeat; .3333.

**Repunit** - an integer consisting only of 1’s.

**Residual** - the observed value minus the predicted value. It is the difference of the results obtained by observation, and by computation from a formula.

**Rhomboid** - a parallelogram having its angles oblique, and its adjacent sides unequal.

**Rhombus** - a quadrilateral whose sides are all the same length (congruent) and whose opposite interior angles are the same size (congruent.)

**Right Angle** - an angle of 90°, one side of the angle is perpendicular to the other side.

**Right Triangle** - a triangle containing an angle of 90 degrees.

**Roman Numerals** - a system of numeration used by the ancient Romans, seven letters of the Roman Alphabet: I, 1; V, 5; X, 10; L, 50; C, 100; D, 500; M, 1000.

**Root** - one of the equal factors that will produce it.

**Root of a Polynomial** - solutions when the polynomial is set equal to zero.

**Root of Unity** - a solution of the equation xn=1, where n is a positive integer.

**Rotate** - to rotate an object in a tessellation means to repeat the object by spinning it on a point a certain angle.

**Round-off Error** - the error accumulated during a calculation due to rounding intermediate results.

**Rounding** - the process of approximating a number to a nearby number.

**Ruled Surface** - a surface formed by moving a straight line (called the generator).

**Rusty Compass** - a pair of compasses that are fixed open in a given position.

I hope that you've enjoyed my list of words that start with R.

~Mary

N * O * P * Q * R * S * T * U * V * W * X * Y * Z

I keep these definitions as a glossary in my binder.

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