MATH DICTIONARY

D

decagon:  a polygon with ten sides.

decimal numbers:  the numbers in the base 10 number system.

decreasing function:  a function is considered to be decreasing if f(b) < f(a) when b > a.

deduction:   a conclusion arrived at by reasoning.

definite integral:  the definite integral of f(x) between a and b represents the area under

the curve y = f(x) , above the x - axis, to the right of the line x = a, and to
the left of the line x = b.   The definite integral of f(x) = F(b) - F(a

where F is an antiderivative function for f(x).

degree:  1/360 of a full rotation.  There are 360 degrees in a circle.  Unit of measure of an

angle.

denominator:  the bottom part of a fraction.

dependent variable:  the output of a function.

derivative:  the rate of change of a function.  The derivative at x of f(x) is the slope of the

tangent line at (x, f(x)).   y' = f ' (x) = [f(x + delta x) - f(x)] / delta x.

determinant:  the determinant | a  b |  =  ad - bc.
| c  d |

diagonal:  the line segment connecting two nonadjacent vertices in a polygon.

diameter:  the line segment joining two points on a circle and passing through the center.

difference:  the result of subtracting two numbers.

differentiable:  a function is differentiable over an interval if it is continuous over the

interval and if the derivative exists everywhere on the interval.

differential:  an infinitesimally small change in a variable, represented by d, as in dx, or dy.

differentiation:  the process of finding a derivative.

digit:  the ten symbols, 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 are digits.  Example:  the number 365

has three digits:  3, 6, and 5.

dimension:  The dimension of a space is the number of coordinates needed to identify a

location in that space.

directly proportional:  y is directly proportional to x if y = kx.

discriminant:  the discriminant of a quadratic equation, ax2 + bx + c = 0 is b2 - 4ac.

The discriminant tells how many roots there are for the equation and the

nature of the roots.

disjoint:  having no elements in common.

disjunction:   an OR statement.

distributive property:  a(b + c) = ab + ac

divergent series:  a series whose sum is infinite.

dividend:  In a / b = c,   a is the dividend.

division:  the opposite operation of multiplication.

divisor:  In a / b = c,  b is the divisor.

dodecahedron:  a polyhedron with twelve faces.

domain:  the set of all possible values of the argument of a function.

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