Download Chapter 9 Signed Numbers

Chapter 9
Signed
Numbers
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
9.2
Subtracting Signed
Numbers
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
Opposite Numbers
The opposite of a positive number is a negative
number with the same absolute value.
The opposite of 4 is – 4.
–5 –4 –3 –2 –1
0
1
4 + (– 4) = 0
10 – 4 = 6
10 + (–4) = 6
15 – 8 = 7
15 + (–8) = 7
12 – 2 = 10
12 + (–2) = 10
2
3
4
5
The sum of a number and
its opposite is zero.
Subtracting is the same
as adding the opposite.
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
Subtraction of Signed Numbers
Subtraction of Signed Numbers
To subtract signed numbers, add the opposite of the
second number to the first number.
Example:
Subtract. –6 – 14
–6 + (–14)
The opposite of 14 is –14.
Change the subtraction to addition.
–20
Perform the addition of the two
negative numbers.
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
Subtraction of Signed Numbers
Example:
Subtract. –21 – (–13)
–21 + (13)
The opposite of –13 is 13.
Change the subtraction to addition.
–8
Perform the addition.
Remember when subtracting two signed numbers:
1. The first number does not change.
2. The subtraction sign is changed to addition.
3. Write the opposite of the second number.
4. Find the result of the addition problem.
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
Subtraction of Signed Numbers
Example:
Subtract. 5  1
11 5
5 1 5  1
Subtraction changed to addition.
    
11 5 11  5 
5 5
1 11
        The LCD is 55.
11 5   5 11
25  11  Multiply the fractions.

 
55  55 
14
Add the fractions.

55
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.
Applied Problems with Signed Numbers
Example:
Find the difference in altitude between a mountain 5628 feet
high and a gorge 350 feet below sea level.
5628 feet
Sea
level
Difference
in
5628 feet – (–350 feet ) = 5978 feet
altitude
350 feet
5628 – (–350) = 5628 + 350 = 5978
Copyright © 2012, 2009, 2005, 2002 Pearson Education, Inc.