Online Math Dictionary: D

Easy to understand math definitions for K-Algebra mathematics
Just scroll down or click on the word you want and I'll scroll down for you!

decagon	decameter	deceleration
decimal	degree of an angle	degree of a polynomial
denominator	diameter	difference
digit	dihedral angle	distributive property
dividend	divisor	dodecagon
dodecahedron

Decagon
A decagon is a ten sided polygon. The picture on the right is a regular decagon since all the sides and angles are the same (congruent.)
For more info, check out Properties of Decagons.

decagon

Decameter
A decameter is 10 meters (in the metric system). The prefix "deca" mean "ten of." In U.S. measurement, a decameter is about 32.808 feet.Deceleration
Deceleration is a slowing down of your speed (velocity). In physics, you just say "acceleration" whether you are speeding up or slowing down... It just means that the speed is changing. Decelerating is slowing down.

Decimal
Decimal numbers are like fractions because they count PART of something. Whole numbers (0, 1, 2, 3, ...) count whole things -- like a whole pizza. You can use a decimal number to count part of the pizza. Half of a pizza would be 0.5 of a pizza. One-fourth of a pizza would be 0.25 of a pizza.
Examples: 2.34 45.009 0.3737373
For more info on decimals, check out my decimal lessons.

Degree of an Angle
A degree is a special unit of measure that measures things that are circular -- like angles that sweep around! To show that a measurement is a degree, you use a little circle after the number.

degree of an angle

Degree of a Polynomial
To find the degree of a polynomial, just find and count the biggest exponents. The green polynomial below is a 3rd degree polynomial because the biggest power is a cube. The purple polynomial below has a degree of 10 since8+2=10 and that's the biggest one.

For more info, check out my algebra lesson on polynomials.

Denominator
The denominator is the bottom number in a fraction.

For more info, check out my lessons on fractions.

2/3 showing that 3 is the denominator

Diameter
The diameter is a chord (a line segment) that passes through the center of the circle. The diameter also cuts across the thickest part of the circle.

diameter = 2 x radius
d = 2r

diameter of a circle

Difference
The difference is the answer you get when you subtract one number from another number.
Example: The difference of 8 and 3 is 5.

For more info, check out my Subtraction Lessons.

Digit
Digits are the numbers we use for counting: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Dihedral Angle
A dihedral angle is the interior angle formed by two planes -- usually in three dimensional geometric figures like polyhedra. In the picture on the right, you can see a dihedral angleon the inside of a cube. The dihedral angle is formed by the bottom face and the left side.

To find the dihedral angles for the different Platonic solids and semi-regular Platonic solids, check out my Polyhedra Gallery.

dihedral angle

Distributive Property of Arithmetic and Algebra
The distributive property of arithmetic and algebra is a math rule that is always true. Here it is with letters:
a ( b + c ) = ab + ac
This property is giving you instruction on how to deal with those parenthesis. Remember that you always do what's in the parenthesis ( ) first... But, in Algebra, you may not be able to add the b and the c... So, this property tells you what to do... You distribute the a to the b and, then you distribute the a to the c.

Here it is with numbers so you can check this for yourself!
2 ( 3 + 4 ) = 2x3 + 2x4
Remember your order of operations: Parenthesis, then multiplication, then addition!

Dividend
In a division problem, the dividend is the number you are dividing INTO. In the problem below, the 6 is the dividend.

For more info, check out my Division Lessons.

Divisor
In a division problem, the divisor is the number you are dividing BY. In the problem below, the 3 is the divisor.

For more info, check out my Division Lessons.

Dodecagon
A dodecagon is a twelve sided polygon. The picture on the right is a regular dodecagon since all the sides and angles are the same. (congruent.)
For more info, check out Properties of Dodecagons.

dodecagon

Dodecahedron
A dodecahedron is a 3 dimensional geometric figure (a polyhedron) that is made up of 12 regular pentagons. The dodecahedron is one of five very famous objects called The Platonic Solids.
     Properties of the dodecahedron:
     12 faces: regular pentagons
     20 vertices
     30 edges
     Dihedral angle: about 116.56 degrees

For more info about Platonic solids, check out my Platonic solids gallery.

dodecahedron

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