Online Math Dictionary: I

Easy to understand math definitions for K-Algebra mathematics
Just scroll down or click on the word you want and I'll scroll down for you!
 

icosahedron icosidodecahedron identity
additive identity
identity
multiplicative identity
imaginary number improper fraction
inequality infinite infinity
inscribed integer intersection
intersection of sets inverse
additive inverse
inverse
multiplicative inverse
irrational number isosceles triangle isosceles trapezoid

 

Icosahedron
An icosahedron is a polyhedron made up of twentyequilateral triangles.  It is one of the five Platonic Solids.
     
20 faces: equilateral triangles
     12 vertices
     30 edges
     Dihedral angle: about 138.19 degrees

For more info about Platonic solids, check out myPlatonic solids gallery.

icosahedron

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Icosidodecahedron
An icosidodecahedron is a polyhedron - one of the thirteen semi-regular Platonic solids.  It's
 created by either cutting (truncating) the dodecahedron one half of the way into each side or cutting (truncating) the icosahedron one half of the way into each side.
     32 total faces: 20 equilateral triangles and 
                                 12 regular pentagons
 
     30 vertices: 2 triangles and 2 pentagons
     60 edges
     
Dihedral angle: about 142.623 degrees

For more info about Platonic solids, check out myPlatonic solids gallery.

icosidodecahedron

 

Identity - Additive Identity
In basic arithmetic, the additive identity is the number 0...  Because you can ADD 0 to any number and that number keeps its identity (it stays the same).
Example:   5 + 0 = 5

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Identity - Multiplicative Identity
In basic arithmetic, the multiplicative identity is the number 1...  Because you can MULTIPLY 1 to any number and that number keeps its identity (it stays the same).
Example:   3 x 1 = 
3

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Imaginary Number
The regular numbers you usually work with are from the Real Number System.  But, there is another kind of number - an imaginary number.  Imaginary numbers are in the form:
 
5i and -8i where i = sqrt(-1)
For more info on imaginary numbers, check out my lessons on complex numbers.

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Improper Fraction
There's really nothing "improper" about them and we use them in algebra and higher math all the time.  An improper fraction is when the numerator is greater than or equal to the denominator.
For more info on improper fractions and how to change them into mixed numbers, check out my lesson onimproper  fractions.

10/3

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Inequality
An inequality is like an equation, but without the "equals" sign.  Instead, it has one of these signs:
                                                                    inequality signs
Examples:     5 > 3       2x + 7 <  -9

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Infinite
An infinite list of numbers goes on forever and ever and never stops.
Example:  The whole numbers:  0, 1, 2, 3, 4, ...

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Infinity
Here is the official symbol for infinity...  It's a "figure eight" laying on its side.
                                                                                      infinity

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Inscribed
Example:  The picture on the right...  The circle is said to be inscribed in the triangle since the circle is inside so that its edge (circumference) is just touching each of the sides of the triangle.
A circle inscribed in a triangle

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Integer
An integer is one member of this set:  { ... , -3, -2, -1, 0, 1, 2, 3, 4, 5, ... }

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Intersection
An intersection is the place where two things cross.
intersecting lines

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Intersection of Sets
The intersection of two sets is a set of elements that appears in both sets.
Example:    A = { 1, 2, 3, a, b, c }     B = { 3, 4, 5, b, c, f, g }
The intersection of sets A and B = { 3, b, c }

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Inverse - Additive Inverse
The additive inverse of a number, a, is the number, -a, you add to it to get 0 (the additive identity).
                                                              + (-a) = 0
Examples:  The additive inverse of 8 is -8 since 8 + (-8) = 0
             The additive inverse of -2 is 2 since -2 + 2 0

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Inverse - Multiplicative Inverse
The multiplicative inverse of a number, a, is the number, 1/a, that you multiply it to so you get 1 (the multiplicative identity).
                                a x (1/a) = 1   and 5 x (1/5) = 1
Example:  The multiplicative inverse of 5 is 1/5.
            The multiplicative inverse of 1/2 is 2.

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Irrational Number
An irrational number is a number whose decimal part goes on forever and ever without repeating.
                pi  = 3.1415926...    and    sqrt(7) = 2.645751...

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Isosceles Trapezoid
An isosceles trapezoid is a trapezoid whose sides are the same length (congruent.)

For more info on trapezoids, check out my Properties of Trapezoids page.

isosceles trapezoid

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Isosceles Triangle
An isosceles triangle is a triangle with two equal sides.

For  more info on triangles, check out my Properties of Triangles page.

isosceles triangle

 

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