NS 2'3 Subtracting Integers

1
NS 2.3 Subtracting Integers

• STANDARD

2
OBJECTIVE

• STUDENTS WILL BE ABLE TO
• Subtract integers using the number line
• Subtract integers using the rules

3
Subtracting Integers Using the Number Line

• ?-----l-----l-----l-----l-----l-----l-----l--?
• -3 -2 -1 0 1 2 3
• When using the number line, you move the
  opposite way from the sign of the number being
  subtracted
• -3 (-2)
• -1
• 1 (2)
• -1
• So, if you start at -3 and subtracting a -2, you
  are going to move 2 units towards the positive.

4
Practice Subtracting Integers

• -4 7
• -11
• 6 (-2)
• 8
• -12 (-5)
• -7
• 6 9
• -3

5
Addition Vs. Subtraction

• What is the difference between
• 7 3 and 7 (-3) ?
• 7 3 4 and 7 (-3) 4
• The only difference is that 7 3 is a
  subtraction problem and 7 (-3) is an addition
  problem.
• So, SUBTRACTING IS THE SAME AS ADDING THE
  OPPOSITE
• Thats why when we use the number line,
  we are moving in the opposite direction of the
  sign.

6
Subtracting Integers Rule

• When subtracting, change the subtracting to
  adding the opposite or think of
  keep-change-change and then follow your addition
  rules!
• So, keep the sign of the first integer, change
  subtraction to addition, change the 2nd integers
  sign to the opposite sign, then your problem
  becomes a addition problem!!
• Example 1 - 4 (-7)
• - 4 (7)
• k c c
• ?Different signs subtract, keep sign of
  larger
• 3
• Example 2 - 3 - 7
• - 3 (-7)
• k c c
• ?Same signs add, keep the sign
• -10

7
Practice the Subtraction Rule

• -8 (4)
• -12
• -11 (-2)
• -9
• 7 (-6)
• 13
• 13 20
• -7

8
Lets Review

• 1. If your problem is addition, follow the
  addition rule.
• -same signs add and keep
• - different signs subtract, keep sign of the
  larger number
• 2. If your problem is subtraction, change
  subtraction to adding the opposite
  (keep-change-change) and then follow the addition
  rule.

9
Addition Rule Song

• Sing to Row, row, row, your boat
• Same signs add and keep,
• Different signs subtract,
• Keep the sign of the larger number,
• Then it will be exact!!