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/s^{2} (“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)

**Add**

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

**Addend**

Any of the numbers that are added together.

**Addition**

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

**Additive Identity**

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

a + 0 = 0 + a = a

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

**Adjacent**

Lying next to each other.

**Adjacent Angles**

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

**Adjacent Faces**

Faces that share a common edge.

**Adjacent Side (triangle)**

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

**Adjacent Sides**

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**

A sequence made by adding the same value each time.

**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.