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1D. 2D, 3D

One-dimensional, two-dimensional, three-dimensional. One-dimensional: able to be identified by one co-ordinate, for example points on a line.

Two-dimensional: requiring two co-ordinates for identification, for example points in a plane. Also used to describe flat geometric shapes.

Three-dimensional: requiring three co-ordinates for identification, for example points in space. Also used to describe solid geometric shapes


Acute Angle

An angle between zero and ninety degrees.


The operation to combine two numbers or quantities to form a further number or quantity, the sum or total. Addition is the inverse operation to subtraction.


The part of mathematics that deals with generalised arithmetic. Letters are used to denote variables and unknown numbers and to state general properties. Example: a(x + y) = ax + ay shows a relationship that is true for any numbers a, x and y. Adjective: algebraic. See also equation, formula, identity and expression.

Alternate Angles

Where two straight lines are cut by a third, as in the diagrams, the angles d and f (also c and e) are alternate.

Alternate Angles

Where the two straight lines are parallel, alternate angles are equal.

Analogue Clock

A clock usually with 12 equal divisions labelled 1 to 12 to represent hours. Each twelfth is subdivided into five equal parts providing sixty minor divisions to represent minutes. The clock has two hands that rotate about the centre. The minute hand completes one revolution in one hour whilst the hour hand completes one revolution in 12 hours.


Where two line segments meet at a point, this term describes the measure of rotation (normally clockwise) from one of the line segments to the other. In this way, a right angle measures 90 degrees, an acute angle is between 0 and 90 degrees, an obtuse angle is between 90 and 180 degrees and a reflex angle is greater than 180 degrees.


A number or result that is not exact. In a practical situation an approximation is sufficiently close to the actual number for it to be useful. Verb: approximate. Adverb: approximately. When two values are approximately equal, the first symbol below is used instead of the normal = sign. If all that's known is the order of magnitude, the second symbol below is used.

Approximate Symbols

For example, there are approximately 365 days in a year (there are 365.25 to be exact, making each fourth year a leap year with 366 days), and the mass of the Sun in kg is known to be roughly 2 with 24 zeroes after it.


A portion of a curve. Often used for a portion of a circle.


A measure of surface. Area is usually measured in square units e.g. square metres.

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