# Mathematics Dictionary : Letter A

Math: the systematic treatment of magnitude, relationships between figures and forms, and relations between quantities expressed symbolically.
Also, mathematical procedures, operations, or properties.

## Dictionary : Letter A

Abacus
An abacus has beads that slide on rods. It can be used to count, add, subtract, multiply and more.
• the column on the far right is for ones (1,2,3,…)
• the next column is for tens (10,20,30,…)
• the next column is for 100s (100,200,300,…)

Abscissa
The horizontal (“x”) value in a pair of coordinates. How far along the point is.

Absolute Error
The difference between the actual and measured value.

Absolute Value
How far a number is from zero.

Acceleration
How fast velocity changes.
Usually measured as m/s2 (“meters per second squared”).

Accuracy
How close a measured value is to the actual (true) value.

Acre
A US Standard Unit of area, usually used to measure land.
– 1 acre = 4,840 square yards.
– 1 acre is about 0.4 hectares in the Metric system, or exactly 4,046.8564224 square meters.

Acute Angle
An angle less than 90° (90° is called a Right Angle)

Acute Triangle
A triangle that has all angles less than 90° (90° is a Right Angle)

To bring two or more numbers (or things) together to make a new total.

Any of the numbers that are added together.

Finding the total, or sum, by combining two or more numbers.

The “Additive Identity” is 0, because adding 0 to a number does not change it
a + 0 = 0 + a = a

What you add to a number to get zero. The negative of a number.

Lying next to each other.

Two angles that have a common side and a common vertex (corner point), and don’t overlap.

Faces that share a common edge.

In a general triangle an Adjacent Side is adjacent (next to) to the angle θ.

Any two sides of a polygon with a common vertex (corner point).

Algebra
Algebra uses letters (like x or y) or other symbols in place of values, and then plays with them using special rules.

Algorithm
A step-by-step solution.

Alternate Exterior Angles
When two lines are crossed by another line (the Transversal), a pair of angles
• on the outer side of those two lines
• but on opposite sides of the transversal
are called Alternate Exterior Angles.

Alternate Interior Angles
When two lines are crossed by another line (the Transversal), a pair of angles
• on the inner side of each of those two lines
• but on opposite sides of the transversal
are called Alternate Interior Angles.

Alternating Series
An infinite series where the terms alternate between positive and negative.

Altitude
The height of an object or place above sea level.

Altitude (geometry)
another word for height.
For Triangles: a line segment leaving at right angles from a side and going to the opposite corner.

AM
The half of the day from midnight to midday. What we call morning.

Amplitude
The height from the center line to the peak (or trough) of a periodic function.

Analog
Something physical with continuous change.

Analog Clock or Watch
A clock or watch is called “analog” when it has moving hands and (usually) hours marked from 1 to 12 to show you the time.

Analogy
A way of thinking about something by comparing it to something else.

And
In logic “and” means that two things must both be true for the statement to be true.

Angle
The amount of turn between two lines around their common point (the vertex).

Angle Bisector
A line that splits an angle into two equal angles.

Angle of Depression
The “downwards” angle from the horizontal to a line of sight from the observer to some point of interest.

Angle of Elevation
The “upwards” angle from the horizontal to a line of sight from the observer to some point of interest.

Annual
Something that happens once a year.

Annual Percentage Rate (APR)
The percentage cost of borrowing per year, including interest, fees, etc.

Annual Percentage Yield (APY)
The annual rate of return on an investment.

Annulus
A flat shape like a ring, or a flattened donut.

Anticlockwise
Moving in the opposite direction to the hands on a clock. Also called Counterclockwise (US English).

Apex
The point (vertex) furthest from the base of an object.

Apothem
The distance from the center of a regular polygon to the midpoint of a side.

Approximation
Not exact, but close enough to be used.

Arc
Part of the circumference of a circle Or part of any curve.

Arc Length
The distance along the arc (part of the circumference of a circle, or of any curve).

Area
The size of a surface.

Argand Diagram
Another name for Complex Plane

Argument
An input to a function: a variable that affects a functions result.

Arithmetic
The basic calculations we make in everyday life: addition, subtraction, multiplication and division.

Arithmetic Mean
Another name for Average.

Arithmetic Progression
Another name for Arithmetic Sequence

Arithmetic Sequence

Arm of an Angle
Any of the two lines that form the angle, as shown.

Array
Items (such as objects, numbers, etc.) arranged in rows and/or columns.

Ascending Order
Arranged from smallest to largest. Increasing.

Asset
Something you own that has value.

Associative Law
When adding it doesn’t matter how we group the numbers (i.e. which we calculate first).

Asymmetry
Asymmetry means “no symmetry”.

Asymptote
A line that a curve approaches, as it heads towards infinity.

Atto-
A prefix meaning one-quintillionth (1/1,000,000,000,000,000,000 or 10-18)

Attribute
A property of an object or person etc.

Autumn
The season that follows summer and comes before winter.

Average
A calculated “central” value of a set of numbers.

Axes
Plural of Axis.

Axiom
A statement that is taken to be true, so that further reasoning can be done.

Axis (geometry)
An imaginary line around which something rotates.

Axis (graph)
A reference line drawn on a graph (you can measure from it to find values).

Axis of Symmetry
A line through a shape so that each side is a mirror image.