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I

Icosahedron

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


Identity

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.

An Identity


Imperial Units

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.


Improper Fraction

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.


Inch

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

1 inch in metric units is approximately 2.54 cm.

Inequality

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.


Integer

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


Intercept

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.


Interior Angle

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


Intersect

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.



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