Transcript Additive Inverses

2-3 Addition of Rational Numbers(pgs 63-70)
2-4 Subtraction of Rational Numbers (pgs71-76)
9N3: Explain effects of operations on magnitude of quantities
9N4: Develop fluency in computation
Vocab
Additive Inverses (2-3)
• Two rational numbers with a sum of 0.
1
1
(examples: -4.2 and 4.2 ,
and 
2
2
Note:
1

2
1
2
1
2
All represent the same quantity
)
Think of the number line for adding
integers
• Add a positive integer by moving to the
right on the number line
• Add a negative integer by moving to the left
on the number line
• Subtract an integer by adding its opposite
Rules for Addition of Integers
1) To add integers having the same sign, add the absolute
value of each number. Keep the same sign. (SAK)
Same-Add-Keep
2) To add integers with different signs, subtract the smallest
absolute value from the largest. Use the sign of the number
with the largest absolute value and. (DSL)
Different-Subtract- Larger
3) Subtract an integer by adding its opposite.
(then follow 1 or 2)
4) Watch out! The negative of a negative is the opposite
positive number.
-(-a) = +a
Examples
• Find the additive inverse
1) 5.7
2)
3) –(-6)
6

-5.7
5
-6
6
5
Add or Subtract
(For HW you must show changing subtraction to adding opposite and
finding common denominator for all fractions)
4) -10 + -15 (SAK or DSL?)
-25
5)
-3 – 8
(change then SAK or DSL)
-11
6) (-5) + 4 +(-12) + 13 (Hint: Combine + and – first)
(-17) + 17
0
7)
4 2

5 5
2

5
8)
1  2

6
9
3 4


18 18

7
18
9) -50 – 3
-53
10)
1 1

12 3

1 4
 
12 12
3
1

12
4
11) -2 –(-5x) + 8x – 3x – (-6)
10x + 4
12) Joe has $86 in his account and writes a check for $95.
How much is in his account?
$86-$95
-$9, He is overdrawn by $9
13) It was 12°F at 6:00 pm at midnight it was -3°F, how
much did the temperature change?
12 – (-3)
15, The temperature changed by 15°
Assignment
• 2-3/68-69/20-42e,50-66eoe
• 2-4/74-75/28-48e,53-60,65e,f