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EnchantedLearning.com Math Dictionary

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D is for ...

decagon A decagon is a ten-sided geometric figure.

deci Deci is a prefix that means one-tenth. For example, a decimeter is one tenth of a meter.

1.33 decimal A decimal is a base 10 number that is written with a decimal point in it. For example, 1.1, 10.43, and 0.01 are decimals.

decimal point A decimal point is a dot that separates the a number into the whole number part (on the left of the decimal point) and the fraction (to the right of the decimal point). For example in 21.46, 21 is the whole number and .46 (forty-six hundredths) is the fraction.

deficient number A deficient number is an integer for which the sum of its proper factors (divisors) is less than the number itself. For example, 9 is a deficient number because the proper divisors of 9 are 1 and 3 which add up to 4, which is less than 9. Compare with abundant number, perfect number.

degree A degree is a measure of temperature or angle. There are 360 degrees in a circle. Each degree is divided into 60 minutes, represented by the apostrophe symbol, '. 1°=60'.

denominator The denominator is the bottom number in a fraction.

Descartes René Descartes ( March 31, 1596 - February 11, 1650) was a French mathematician and philosopher. Descartes invented the Cartesian coordinate system and many principles of philosophy.

diagonal A diagonal is a line that joins two non-consecutive vertices of a polygon.

diameter The diameter is the longest distance from one side of a circle (or a sphere) to the other.

diamond A diamond is a four-sided figure (a quadrilateral) whose sides are all the same length. People play baseball on a diamond-shaped field.

dice Dice are cubes with numbers on each side that are used in games. A single one is called a die.

difference The difference is the answer in a subtraction problem.

digit A digit is a single numeral within a number. For example, the number 153 is a 3-digit number.

dime A dime is a coin worth ten cents.

directrix The directrix is a line that helps generate a parabola or hyperbola. For example, a parabola is a set of points (P) such that the distance from the directrix to P is equal to the distance from P to the focus F.

dividend The dividend is the number that is divided (in long division). The dividend divided by the divisor is the quotient (plus a remainder).

division Division is an operation that divides a number into portions. Any number divided by one is equal to the original number. You cannot divide any number by zero. Division is the inverse of multiplication. In long division, the dividend is divided by the divisor, resulting in a quotient plus a remainder. The ÷ symbol is called an obelus.

divisor The divisor is the number that the dividend is divided by (in long division). The dividend divided by the divisor is the quotient (plus a remainder).

dodecagon A dodecagon is a twelve-sided polygon (figure).

dodecahedron A dodecahedron is a twelve-sided geometric solid whose faces are pentagons.

dollar A dollar is worth 100 cents.

dominoes Dominoes is a game played with tiles that have dots on them.

dot A dot is a tiny speck or point.

**** **** **** 12 dozen Dozen is another word for twelve.

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EnchantedLearning.com Math Dictionary

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Counting

Addition

Subtraction

Multiplication

Division

Number Line

Fractions

Decimals

Graphs

Measurement

Rounding

Click on an underlined word for more information on that subject. If the math term you are looking for is not in the dictionary, please e-mail us.

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