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Octahedron
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
x
2 Do we do
the 4
+ 10
first? Or the
10
x
2 first?
Here is the official order of operations:
(1) Parenthesis
(2) Exponents
(3) Multiplication & Division
(4) Addition & Subtraction
So, for 4
+ 10
x
2, we do
multiplication, then
addition...
4
+ 10
x
2 =
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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Origin
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. |
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Orthogonal
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 the green 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. |
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Oval
An oval is just a stretched
out
circle. An oval is the same thing as an
ellipse. |
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