Radius, Ratio, Ray

I receive ad commissions. See our FTC disclosure. No cost to you.

Order worksheet bundles. Interactive fonts, colors, SIZES. Print or file.

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.

Math Words That Start With R: Supplement your math glossary with the math dictionary that you can print below.

**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.

**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.

**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.

**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 this list of words that start with R. If you'd like a complete math glossary, print our free Math Dictionary to put in your binder or keep at your desk.

~Mary

I print and keep these Math definitions as a glossary in my binder: Free Printable Math Dictionary For Kids.

You can also download it to your tablet or bookmark the page.

See the alphabetical links below for more online Math words.

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

Sample Math practice worksheets. Bundle includes dictionary for Math.

2. One PDF Download. No ads.

3. Filed by topic.

4. Interactive. Printable.

5. Use with any Math Lesson Plans.

6. Addition, Subtraction, Multiplication, Division and Fraction Practice.

Check out our main printable Math worksheets page.