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integers
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Subtraction of Integers
I can subtract positive and negative numbers.
Focus Question
What is the rule for subtracting positive and negative numbers?
The subtraction rule Rule: To subtract ADD the
OPPOSITE. Or – Subtracting is the same as
ADDING THE OPPOSITE.
5 + (-7) = 5 – 7 =
-2-2
Example: -5 - (-3) ADD the OPPOSITE –5 + (3) = -2
Notice the subtraction operation changed to addition, and
the opposite of –3 becomes 3.
NOTE: only the number behind the subtraction sign gets changed.
- 3 – 2
- ADD the OPPOSITE
- 3 – 2
- ADD the OPPOSITE –3 + (-2) = ____-5
Two Negatives 5 - (-3)
Two Negatives 5 - (-3) ADD the OPPOSITE 5 + (+3) Notice the use of the rule. 5 - (-3) = 5 + 3 = 8
-8 –(-4) + 2
ADD the OPPOSITE
-8 –(-4) + 2
ADD the OPPOSITE –8 + (+4) + 2. -8 - (-4) +2 - 8 + 4 + 2 = - 2
Try some with the rule
-8 – (-10)= 4 - 7 = -9 - 5 = -20 – (-4) = 40 – 32 =
Try some with the rule
-8 – (-10)= 4 - 7 = -9 - 5 = -20 – (-4) = 40 – 32 =
-8 + 10 =4 + (-
7)=-9 + (-5)=-20 +
4=40 + (-32)=
2
-3-14
-168
Example: -7 – 9 - (-4) – 3 + 9 - (-4)=
Example: -7 – 9 - (-4) – 3 + 9 - (-4)= Changes on paper to –7 + -9 + 4 + - 3 + 9 + 4 =
Then think DOWN 7, Down 9 more, then UP 4, Down 3, UP 9, and UP 4.
The result is –2.
EXAMPLE 2 Evaluating a Variable Expression
Evaluate 15 – a – b when a = 24 and b = – 36 .
EXAMPLE 2 Evaluating a Variable Expression
Evaluate 15 – a – b when a = 24 and b = – 36 .
15 – 24 – (–36) =15 + (–24) + 36 =
–9 + 36 =
27
Add the opposite of 24 and of –36.
Add –9 and 36.
Substitute 24 for a and –36 for b.
Add 15 and –24.
15 – a – b =
GUIDED PRACTICE for Examples 1, 2, and 3
a – b – (–6) a = 8, b = –15
GUIDED PRACTICE for Examples 1, 2, and 3
8 – (–15) – (-6)
8 + 15 + 6
29
Add the opposite of –15 andof –6.
Substitute 8 for a and –15 for b.
Add.
a – b – (–6) a = 8, b = –15
In the Sahara Desert one day it was 136°F.
In the Gobi Desert a temperature of -50 F was recorded.
What is the difference between these two temperatures?
Write a subtraction expression to represent this situation.
Assignment: No Calculators - show your work
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