Objective(s):
By the end of this lesson the student will be able to:
identify any number's opposite
and be able to add a negative number to a positive one. 
PreClass
Assignment: Review/ completion of Algebra
Lesson 10
Resources/Equipment/Time Required:
Outline:
Additive Inverses are opposites.
Two numbers are opposites if their sum equals zero. For example, 8 and
8 are additive inverses because their sums total zero. This makes them
opposites.
Another way to write the
opposite of –8 is to write –(8). To subtract a negative 8 is the same
as making it a positive 8, or finding its opposite.
You can do the same thing
with variables. For example, (x) = x.
Using this principle, let's
add a negative number to a positive one: 8 + (3) = 8 – 3 = 5. This could
be read as 8 plus a negative 3 OR 8 minus 3 OR 8 plus the opposite
of 3.
In algebra, subtracting a
number can also be described as adding its opposite.
For example, x – y = x +
(y).
OR
8 – (5) = 8 + 5 = 13
Now, let's turn things around
a bit. Try this one:
14 – 28 = x
How can you rewrite that
to use what you've learned about opposites?
14 + (28) = x
–14 = x
Let's try one more:
11 – (3) – 4 = x
11 + 3 – 4 = x
14 – 4 = x
10 = x
Assignment(s)
including Answer key:
1. 5 – 7
2. 8 – (10)
3. – 3 – 7
4. – 7 – 9
5. 7 + (3)
6. 25 – 250
7. 5.8 – 2.3
8. 2.3 – 5.8
9. (34 – 13) – (15 – 17)
10. 11 – 5 – [6 + (13)]
Answer key:
1. –2
2. 18
3. –10
4. –16
5. 4
6. –225
7. 3.5
8. –3.5
9. 23
10 .13
PreRequisite
To: Algebra Lesson
12
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