N

**natural logarithm: the logarithm with the base of e. Written: ln
x.**

**natural numbers: the counting numbers. **

**negative number: a real number less than zero.**

**normal: perpendicular.**

**null set: same as empty set. A set with no
elements.**

**number line: a line on which every point represents a
real number.**

**numeral: a symbol that stands for a number.**

**numerator: the top of a fraction.**

**obtuse angle: an angle whose measure is greater than 90
degrees.**

**obtuse triangle: a triangle with an obtuse angle.**

**octagon: a polygon with 8 sides.**

**octahedron: a polyhedron with 8 faces.**

**octal number: a number in base 8.**

**odd function: a function that satisfies the property
that f(-x) = -f(x).**

**odd number: a whole number that is not divisible
by 2.**

**open interval: an interval that does not contain
both its endpoints.**

**ordered pair: a set of two numbers in which
the order has an agreed upon meaning.
Such
as the cartesian coordinates (**

** coordinate
represents the horizontal position, and the second coordinate **

** represents
the vertical position.**

**ordinate: the second coordinate of a cartesian ordered
pair.**

**origin: the point (0, 0) on a Cartesian Coordinate System.**

**orthocenter: the point in a triangle where the three
altitudes intersect.**

**orthogonal: perpendicular.**