Maths Terms for 11-13 Yr Olds

A polyhedron with 20 faces. In a regular icosahedron all faces are equilateral triangles.

An equation that holds for all values of the variables, as opposed to a normal equation which has only one or two fixed solutions. An equals sign with three horizontal lines rather than two is sometimes used when writing an identity. For example the identity below is true no matter what the values of a and b are.

A unit of measurement system historically used in the United Kingdom and other English speaking countries. Units include inch, foot, yard, mile, acre, ounce, pound, stone, ton, pint, quart and gallon. Now largely replaced by metric units.

An improper fraction has a numerator that is greater than its denominator. Example: 9/4 is improper and could be expressed as the mixed number 2 1/4.

Symbol: in. An imperial unit of length. 12 inches = 1 foot. 36 inches = 1 yard. 

Statements such as b > c are inequalities.

They differ from equations in that they don't have equals signs and don't have fixed solutions, only boundary solutions. For example in the above it is known that b must be at least greater than c, but how much greater is not known. Boundary solutions to inequalities can be indicated graphically using shading.

Any of the positive or negative whole numbers and zero. Examples: -2, -1, 0, +1, +2. As opposed to decimal numbers.

The value of the non-zero coordinate of the point where a line on a graph cuts an axis. The y intercept is given the symbol c in straight line graphs of the form y = mx + c.

At a vertex of a polygon, the angle that lies within the polygon.

To have an intersect is to have a common point or points. Examples: Two intersecting lines intersect at a point; two intersecting planes intersect in a line.