Mathematics Glossary

Argand diagram – a graphical way of representing complex numbers in two dimensions where the real component is on the horizontal axis and the imaginary component is on the vertical axis.

Bisect – to split evenly in two. The resulting locus is a line called the bisector. If two points are bisected the bisector is equidistant from the two points. If a line is bisected the result is a line perpendicular to the bisected line and which passes through the line's midpoint. If an angle is bisected the angle is split evenly in two; the bisector is equidistant from the two original lines that make the angle.

Bisector – a line equidistant from two other lines or points.

Cartesian plane – a graphical way of representing points in two dimensions so that the x value is on the horizontal axis and the y value is on the vertical axis.

Centroid – the barycentre, or centre of mass of a triangle, found by taking a line from each vertex of the triangle to the midpoint of the opposing side; see Triangle Centres. Barycentre is also used in astronomy.

Circle – a two dimensional locus equidistant from a point marking its centre.

Circumcentre – the point in a triangle that is the centre of the circumcircle; see Triangle Centres.

Circumcircle – the circle drawn outside a triangle, so that the circle touches all three points of the triangle; see Triangle Centres.

Counting numbers – see natural numbers below.

Cyclic quadrilateral – a quadrilateral which has all its vertices lie on a single circle.

Denominator – the number of the bottom of a fraction. (I remember it because denominator starts with d for down.)

Dividend – a number which divided by a divisor makes a quotient.

Divisor – the number which divides a dividend to make a quotient.

Factor – numbers which are multiplied together; two or more factors multiply together to make a product.

Improper fraction – a fraction with the numerator larger than the denominator. For example, ⁸/₃.

Incentre – the point in a triangle that is the centre of the incircle; see Triangle Centres.

Incircle – the circle drawn inside a triangle, so that the circle touches all three sides of the triangle; see Triangle Centres.

Integers – all natural numbers, zero, and negative versions of all of them as well: ..., -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, ...; see Number Sets.

Irrational numbers – numbers which cannot be made as a fraction; see Number Sets.

Locus – a set of points, which often make up a line or curve. Do not confuse with locust, a type of grasshopper insect.

Mean – the arithmetic mean of a dataset is the sum of the values divided by the number of values.

Median – the middle number of a dataset when the dataset's values are in order. In a dataset with an even number of values, the median is the mean of the two middle values.

Median of a triangle – a line which goes from a vertex (corner) of a triangle to the middle of the opposite side.

Natural numbers – the numbers from 1 upward: 1, 2, 3, 4, 5, ...; see Number Sets.

Numerator – the number on the top of a fraction.

Oblong – a non-square rectangle.

Orthic triangle – the triangle made by joining the base points of the altitudes of the triangle; see Triangle Centres.

Orthocentre – the point found by taking the perpendicular line through each side of the triangle which passes through the opposing vertex of the triangle; see Triangle Centres.

Parallelogram – a four sided polygon with two pairs of parallel sides. Parallelograms are a subset of trapeziums.

Perimeter – the outer edge of a shape, or the distance around the outside of the shape.

Polygon – a many-sided 2D shape; see Polygons.

Polyhedron (pl. polyhedra or polyhedrons) – a many-sided 3D object; see Polyhedra.

Prime number – a number which only has the factors 1 and itself; see Prime Numbers. The "1 and itself" necessarily implies that 1 is not a prime number.

Product – the result of multiplying numbers together; two or more factors multiply together to make a product.

Quadrilateral – a four sided polygon.

Quotient – the result of dividing a dividend by a divisor.

Rational number – a number which can be made as a fraction; see Number Sets.

Rectangle – a quadrilateral with two pairs of parallel sides and all right angles. Rectangles are a subset of parallelograms. A rectangle may also be a square; a non-square rectangle is called an oblong.

Regular – a regular polygon has all its sides the same length and all its angles the same size. For example, a regular quadrilateral is called a square. A regular polyhedron has all its faces the same regular polygon. There are just five different regular polyhedra, known as the Platonic solids.

Rhombus – a quadrilateral with all sides the same length.

Sieve of Eratosthenes – a method of finding prime numbers; see Prime Numbers.

Square – a regular quadrilateral. That is, a quadrilateral which has all sides the same length and all angles the same size. Squares are subsets of rectangles and rhombuses.

Sum – the result of adding two or more numbers together, or sometimes the process of doing the adding.

Tangent – a line that touches a curve (such as a circle) at one point only. A tangent to a circle is perdendicular to the radius at the point where the tangent touches the circle.

Triangle – a three sided polygon; see Triangles.

Trapezium – a quadrilateral with a pair of parallel sides.

Vertex (pl. vertices) – a point or corner of a polygon.

Whole number – the numbers from 0 upward: 0, 1, 2, 3, 4, ...; see Number Sets.