n
A letter often used as a variable for an unknown number, especially a whole number or a position in a sequence.
n-gon
A polygon with n sides, used when the number of sides is general or large, such as a 12-gon.
Natural logarithm
A logarithm with base e (about 2.718), written ln x.
Natural numbers
The counting numbers 1, 2, 3, 4, …, each found by adding 1 to the one before. Some books also include 0.
Negative correlation
A relationship in which one variable tends to decrease as the other increases.
Negative exponent
An exponent less than 0. A negative exponent means the reciprocal: x⁻ⁿ = 1/xⁿ.
Negative integer
An integer less than 0, such as −1, −2 or −3.
Negative number
Any number less than 0, written with a minus sign, such as −4 or −2.5. It lies to the left of 0 on a number line.
Negative reciprocal
The reciprocal of a number with the opposite sign, such as 2 and −½. Perpendicular lines have slopes that are negative reciprocals.
Negative slope
The slope of a line that falls from left to right. Its value is less than 0.
Net
A flat pattern that can be folded to make a solid figure.
Nickel
A US coin worth 5 cents, or $0.05.
Nonagon
A polygon with nine sides and nine angles.
Noncollinear
Points that do not all lie on the same straight line. Three noncollinear points form a triangle.
Nonlinear function
A function whose graph is not a straight line, such as y = x².
Nonnegative
Greater than or equal to 0: zero or positive.
Noon
12 o'clock in the middle of the day, written 12:00 p.m. It separates a.m. from p.m.
Normal distribution
A symmetric, bell-shaped distribution where the mean, median and mode are equal and most values cluster near the center.
Not equal to
The symbol ≠, which shows that two values are not the same.
nth root
A number that, used as a factor n times, gives the original number. The 4th root of 16 is 2 because 2 × 2 × 2 × 2 = 16.
Null hypothesis
In statistics, the starting claim of no effect or no difference, written H₀, that a test tries to find evidence against.
Null set
Another name for the empty set, the set with no elements, written ∅ or { }.
Number bonds
A diagram showing how a whole number splits into two parts, such as 10 = 6 + 4.
Number line
A straight line with numbers placed at equal intervals, used to show and compare numbers.
Number patterns
Sequences of numbers that follow a rule, such as adding 5 each time.
Number sentence
An equation or inequality written with numbers and symbols, such as 8 + 5 = 13 or 6 > 2.
Numeral
A symbol or group of symbols that names a number. Seven can be written with the numerals 7 or VII.
Numerator
The number above the fraction bar. It tells how many of the equal parts are being counted.
Numerical expression
An expression made only of numbers and operation symbols, with no variables, such as 4 × (6 − 2) + 1.