Download Subtracting Integers

Section 2.3
Subtracting Integers
To subtract integers, rewrite the subtraction problem
as an addition problem. Study the examples below.
9
5=4
9 + (-5) = 4
Since both expressions
equal 4, we can say
9
5 = 9 + (-5) = 4
Martin-Gay, Prealgebra, 5ed
2
Subtracting Two Numbers
If a and b are numbers,
then
a b = a + (-b).
To subtract two numbers, add the first
number to the opposite (called additive
inverse) of the second number.
Martin-Gay, Prealgebra, 5ed
3
subtraction =
first
number
+
opposite of
second
number
7–4
=
7
+
(-4)
=
3
-5 – 3
=
-5
+
(-3)
=
-8
3 – (-6)
=
3
+
6
=
9
-8 – (-2)
=
-8
+
2
=
-6
Martin-Gay, Prealgebra, 5ed
4
Adding and Subtracting Integers
If a problem involves adding or subtracting more
than two integers, rewrite differences as sums and
add. By applying the associative and commutative
properties, add the numbers in any order.
9 - 3 + (-5) - (-7) = 9 + (-3) + (-5) + 7
6 + (-5) + 7
1+7
8
Martin-Gay, Prealgebra, 5ed
5
Evaluating Algebraic Expressions
Evaluate x - y for x = - 6 and y = 8.
Replace x with - 6 and y with 8 in x - y.
x
-
y
= (- 6 ) - ( 8)
= (- 6 ) + ( - 8)
= - 14
Martin-Gay, Prealgebra, 5ed
6