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### A Glossary of Mathematical Terms - D

#### Decagon

A ten-sided polygon.

#### Decimal

Decimals are numbers with decimal points.

#### Decimal fraction

A fraction whose denominator is a power of 10.

See Fraction

#### Diagonal

In polygons: a segment connecting two non consecutive vertices.

See Subtraction.

#### Digit

Digits are the symbols used to write numerals in a number system: in the usual (base10) system they are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.

#### Dilation (Dilatation)

A geometric transformation where figures are enlarged or reduced.

#### Discount

A percentage subtracted from a number.

#### Disjoint sets

Sets that have non common elements.

#### Distributive property

A property that links two operations (e.g. addition and multiplication betwen numbers: a(b+c)=ab+ac).

See Division

#### Divisibility rules

Patterns that allow us to determine wheter or not a number divides evenly into another number, without actually doing the division.

#### Division

6 divided by 2: 6/2;
the quotient of 6 and 2 is 3: 6/2=3
the ratio of 6 to 2 is 3: 6/2=3;
the outcome of the division is the quotient;
the first term is the dividend;
the second term is the divisor.

#### Divisor

See Division and Factor.

#### Dodecagon (Duodecagon)

A twelve-sided polygon.

first published on september 01 2003 - last updated on september 01 2003