Mathematical "D" Words
decagon A ten-sided polygon.
decimal notation The notation in which numbers are written using ten digits and each place stands for a power of ten.
decimal system The system in which numbers are written in decimal notation.
deduction The process of making justified conclusions.
definition A description that clearly and uniquely specifies an object or a class of objects.
degree A unit of measurements equal to 1/360 of a complete circle.
of a major arc ACB of circle O
degree measure of minor arc AB of circle O The measure of the central angle AOB.
The divisor, or bottom number, in a fraction.
Remember that a fraction is a division problem. The top number, the numerator, is the number being divided, the fraction bar is the division symbol, and the bottom number, the denominator, is the number of equal parts that you are dividing the top into.
The property that between two elements of the set there is at least one
other element of the set.
of a polygon
A segment that connects two vertices of the polygon but is not a side
of a polygon.
of a circle or sphere
A segment connecting two points on the circle or sphere and containing
the center of the circle or sphere, also the length of that segment.
difference The answer to a subtraction problem.
digit One of the ten symbols, 0 1 2 3 4 5 6 7 8 9, used to write numbers from zero to nine.
The angle formed by the union of two half-planes with the same edge.
dimensions The lengths of the sides of a rectangle. The number of rows and the number of columns in a rectangular array.
dimensions of a box The lengths of three edges of the box which meet at the same vertex. Usually referred to as length, width, and height.
dimensions of a rectangle The lengths of two sides of the rectangle which meet at a single vertex. Usually referred to as length and width.
of translation The
direction given by the vector from any preimage point to its image point
in a translation.
directly congruent Figures which are congruent and have the same orientation.
discrete figure A figure made up of points with space between them.
discrete geometry The study of points as dots separate from each other, and lines made up of these points.
display The area on a calculator where numbers appear.
between two parallel lines The
length of a segment that is perpendicular to the lines with an
endpoint on each of the lines.
distance between two parallel planes The length of a segment perpendicular to the planes with an endpoint in each plane.
between two points
The absolute value of the difference of their coordinates on a coordinatized
from a point to a line
The length of the perpendicular segment connecting the point to
from a point to a plane The
length of the perpendicular segment from the point to the plane.
Property of Multiplication over Addition
For any numbers a, b,
and x : ax + bx = ( a + b )x and x( a + b) = xa
+ xb. Also called distributivity.
Property of Multiplication over Subtraction
For any numbers a,
b, and x : ax + bx = ( a - b )x and ( a - b ) = ax - bx. Also
The number in
a quotient which is being divided; a is the dividend in a/b.
The number by which you divide in a quotient; b is the divisor
in a/b. Also a number that exactly divides into
another number, referred to as a factor.
dodecagon A polygon with twelve sides.
dodecahedron A polyhedron with twelve faces.
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