Algebra I
SECTION 2.3
SUBTRACTING REAL NUMBERS
OBJECTIVES: DEFINE SUBTRACTION IN
TERM OF ADDITION AND SUBTRACT
NUMBERS WITH LIKE AND UNLIKE SIGNS.
Warm-up
Find the opposite of each number.
1. -9
2.
3.7
3.
0
4. 
1
3
Find each sum.
5. -5 + 8
3 2
6. -13 + (-6) 7.  
5 5
8. 6.9 + (-4.28)
Evaluate.
9. 15 · 2 – 7
10. [3(4 – 2)²] +7
11. 12 + 3² + (9 – 6)
Basic Mathematical Operations
+
·
÷
^
√
Definition of Subtraction
For all real numbers a and b:
a – b = a + (-b)
Example: Use the definition of subtraction to evaluate each
difference.
a. -10 – (-10)
b. -5.8 – 4.8
c. 2 1   1 3 
4  4
Practice: P69 Try This after example #2
Homework Check and Questions
Measuring Distance on a Number Line
The distance between two points a and b on a number line:
|a – b| or |b – a|
Example: Find the distance between - 4 and -10 on a
number line.
Practice: P69 Try this at bottom of page.
Example: Let a = 2, b = 3, and c = -5. Evaluate each
expression.
1. a + (-b)
2. (a + b) + (-a) + (-b)
Practice: P65 #58-62e, Pg 70 #50-54e
If Time: P70#’s 5-15
Homework: p70 #’s 17-63o