Online Math Dictionary: O

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!

oblique angle oblique prism oblique triangle
obtuse angle obtuse triangle octagon
octahedron odd numbers order of operations
ordered pair origin orthogonal


Oblique Angle
An oblique angle is an angle that is not aright angle.  (An oblique angle is an angle whose measure is not 90 degrees.)

oblique angles

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Oblique Prism
An oblique prism is a prism that is tilted or slanted a bit.  Technically, an oblique prism is one whosesides do not form 90 degree angles with the bases.

oblique prism

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Oblique Triangles
An oblique triangle is a triangle that is not a right triangle.  (An oblique triangle does not have a 90 degree angle.)

oblique triangles

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Obtuse Angle
An obtuse angle is an angle whose measure isgreater than 90 degrees.

obtuse angle

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Obtuse Triangle
Obtuse triangles aren't very smart.  (Look up "obtuse" in the dictionary!)

Obtuse triangles have one angle that is greater than 90 degrees.  (Obtuse triangles have one obtuse angle.)

obtuse triangle


An octagon is a eight sided polygon.  The picture on the right is a regular octagon since all the sides and angles are the same.  (congruent.)  
For more info, check out Properties of Octagons.


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An octahedron is a 3 dimensional geometric figure (a polyhedron) that is made up of 8 equilateral triangles.  The octahedron is one of five very famous objects called The Platonic Solids.
     Properties of the octahedron:

     8 faces: equilateral triangles
     6 vertices
     12 edges
     Dihedral angle: about 109.47 degrees

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


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Odd Numbers
An odd number is a number that is not even -- meaning that an odd number is NOT cleanly divisible by 2.  (When I say "cleanly divisible" I mean that there's no remainder.)  So, when you divide an odd number by 2, you'll always get a remainder of 1.
Example:  1, 3, 5, 7, ...

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Order of Operations
Order of operations tells us what order we are supposed to do things in a math problem.  For example, what's the answer to this?  4 + 10  Do we do the 4 + 10 first?  Or the 10 2 first?
Here is the official order of operations:
   (1) Parenthesis   (2) Exponents   (3) Multiplication & Division   (4) Addition & Subtraction
So, for 4 + 10 2, we do multiplication, then addition...  4 + 10 = 4 + 20 = 24.
A common phrase to remember the order is: Please Excuse My Dear Aunt Sally.

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Ordered Pair
An ordered pair is a set of two numbers in the form:  (x, y)     Example:  (2, -3) 
Ordered pairs are used in Cartesian coordinates.

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The origin is the point (0, 0) on the Cartesian plane.  It's called the origin because it's the starting place when you plot a point.

origin on the Cartesian plane

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The official definition for orthogonal gets pretty messy pretty fast, so I'm just going to give a really basic explanation:

Orthogonal is like "perpendicular" but, it means more than that...  Look at thegreen line in the pic on the right.   It is orthogonal because it's perpendicular from more that one view...  It's perpendicular to the surface from any way you look at it.  You can walk all the way around the green line and it will always be perpendicular.

They start using this word in Calculus 3 (when working with surfaces).  The real purpose is so people think you are really smart when they walk by the classroom and overhear the lecture.

orthogonal vectors on an ellipsoid

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An oval is just a stretched out circle.  An oval is the same thing as an ellipse.



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