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Eighth Grade
Math Vocabulary
Adjacent
Angles that have a common vertex and
a common side
<1 and <2 are adjacent
Examples
<3 and <4 are adjacent
3
<5 and <6 are adjacent
5
6
4
Alternate Exterior
Angles
A pair of angles on the outer sides of two lines cut by a
transversal, but on opposite sides of the transversal
Examples
<1 and <8 are
alternate exterior
<2 and <7 are
alternate exterior
1
2
8
7
Alternate Interior
Angles
A pair of angles on the inner sides of two lines cut by a
transversal, but on opposite sides of the transversal
Examples
<3 and <6 are
alternate interior
<4 and <5 are
alternate interior
3
6
4
5
Complementary
Two angles whose measures have a sum of 90°
Examples
2
Complementary
1
2
<1 and <2 are complementary
 1  25=
<2=65
<1 + <2 = 90
1
Corresponding
Angles that are on the same side of the transversal and
are both above or both below
the lines cut by the transversal
Examples
<1 and <5 are
corresponding
1
<2 and <6 are
corresponding
<3 and <7 are
corresponding
<4 and <8 are
corresponding
2
3 4
5
6
7 8
Cost per unit
A unit rate used to compare costs per single item
A rate in which the second quantity is one
Examples
$3.90
$0.39
If a pack of 10 markers costs

$3.90, one marker costs $0.39 10 markers 1 marker
Unit Cost  $0.39
If a 12-pack of coke costs $2.76
One coke costs $0.23
2.76 x

12
1
x  .23
$2.76
$0.23

12 cokes 1 coke
Unit Cost  $0.23
If 20 ounces of bottled water
costs $1.00 (100 cents)
then one ounce costs 5 cents
$1.00
$0.05

20 ounces 1 ounce
Unit Cost  5 cents
Dilation
A transformation that enlarges or reduces a figure
by some scale factor,
but does not change its shape
Examples
Each side of the blue triangle
Is half the length
of the side of the
red triangle
The large tree is
Four times as
Tall and wide
As the small tree
Distance Formula
The distance d between any two points  x1 , y1  and  x2 , y2 
is
2
2
d   x2  x1    y2  y1 
Examples
The distance between
(-3,2) and (0,-2) is:
d  ((3)  0)2  (2  (2))2
 3  (4)
2
 9  16
2
(-3,2)
5
4
 25
5
3
(0,-2)
Distributive Property
The property which states that
multiplying a sum by a number
gives the same result as multiplying each
addend by the number
and then adding the products
a (b + c) = a x b + a x c
2( x  3)  2 x  6
4( x  1)  4 x  4
Examples
2(m  3n)  2m  6n
10(3x  y )  30 x  10 y
Experimental
Probability
The ratio of the number of times the event actually
occurs to the total number of trials
or times the activity is performed
(The theoretical probability would predict how
many times the event should occur)
Example
A coin is tossed 50 times with a result of
27 heads and 23 tails.
The experimental
probability of heads
27
is
or 54%.
50
(The theoretical probability of heads is
25
or 50%)
50
Exterior
The angles on the outer sides
of two lines cut by a transversal
Examples
<1, <2, <7 and <8 are exterior angles
( <3, <4, <5 and <6 are interior angles)
Infinite
Having no end or limit, without bound, uncountable
Examples
The set {1, 2,3, 4,5,...} has an
infinite number of elements
The set {2, 4, 6,8,...} has an
infinite number of elements

The number of points
on a line
is infinite
is the symbol for infinity
Intercept
The point where a graph crosses the axis
The y-intercept of the line y = mx+b is b
Example
y=3x+3
y
y-intercept:3
x
x-intercept:-1
Interior
Angles on the inner sides of
two lines cut by a transversal
Example
<3, <4, <5 and <6 are interior angles
( <1, <2, <7 and <8 are exterior angles)
Line of best fit
(conceptual)
A straight line that best fits the data on a scatter plot
(This line may pass through some, none, or all of the points)
Examples
Nonlinear equation
A function whose graph is not a straight line
Examples
yx
2
y x
y  x3
Perfect Square
A number that has integers as its square roots
Examples
49  7  7 is a perfect square because
49  7
81  9  9 is a perfect square because 81  9
1  11 is a perfect square because 1  1
12 is NOT a perfect square because 12  3.46
Pythagorean Theorem
In a right triangle,
the sum of the squares of the length of the legs
is equal to the square of the length
of the hypotenuse:
5
a 2  b2  c2
13
3
5
4
32  42  52
9  16  25
12
52  122  132
25  144  169
15
17
8
82  152  17 2
64  225  289
Scientific notation
A method of writing very large or very small numbers
by using powers of 10
Examples
The Andromeda Galaxy
contains at least
The diameter of an atom
200,000,000,000
of gold is about
or 2.0 X 1011 stars
.0000000025 or 2.5X10-9 inches
Sequences
An ordered list of numbers or objects called terms
Examples
Arithmetic Sequence:
The difference between
any two consecutive
terms is always the same:
Geometric Sequence:
The ratio of any two
consecutive terms
is always the same:
5,8,11,14,17,20,…
5,10,20,40,80,160,…
The common
difference is 3
The common ratio is 2
Slope intercept form
A linear equation written in the form y  mx  b
Where m represents slope and
b represents the y-intercept
Examples:
y  x  2
y  x3
slope = -1
y-int = 2
slope = 1
y-int = -3
y  2x  3
slope = 2
y-int = -3
Square root
One of the two equal factors of a number
Examples
4  2 because 2  2=4
and
4  2 because  -2    -2  =4
36  6
4
(6 and -6)
Since 10 10  100 and  10    10   100
100  10 (10 or -10)
Supplementary
Two angles whose measures have a sum of 180°
Two adjacent angles whose
exterior sides form a straight line
Examples
124  56  180
 A  90  B  90
 A  B  180
 A and  B are supplementary
40 140  180
Theoretical probability
The ratio of the number of
equally likely outcomes in an event
to the total number of possible outcomes
A number used to describe
the chance of an event occurring
Tennessee
What is the probability
that if you randomly choose
a letter in the word Tennessee
You will choose an e?
You can choose 4 e’s
out of 9 letters
4/9 or about 44.4%
Examples
The probability of rolling
an even number on a
six-sided number
cube is 3/6 or ½ or 50%:
There are three even
numbers (2,4,6) out of
six possible outcomes
(1,2,3,4,5,6)
Vertical Angles
A pair of opposite congruent angles formed by
intersecting lines
Angles 1 and 2 are vertical
Examples
The two
3
1
2
138 angles are vertical
138
52
52
138
4
Angles 3 and 4 are vertical
The two
52
angles are vertical
Vertical Line test
yx
2
A way of testing a graphed relation
to determine if it is a function:
“If a vertical line passes through
more than one point on the graph,
then the relation is not a function”
x2  y 2  9
Examples
Each vertical line passes
Through only one point,
So, y=x2 is a function
Vertical lines pass
through more than one point,
So, x2 + y2 =9 is not a function