Be Able to Subtract One Signed Number from Another

9.2 Subtracting Signed Numbers (575)

Objectives:

Be able to subtract one signed number from another

Solve problems involving both addition and subtraction of signed numbers

Solve simple applied problems that involve the subtraction of signed numbers

9.2.1 Subracting One Signed Number from Another (575)

If you look at two numbers whose value is the same, but have different signs, they are called additive inverses. e.g. 4 and -4; 1/2 and -1/2 . Note the sum of them is zero

SUBTRACTION OF SIGNED NUMBERS: To subtract signed numbers add the additive inverse of the second number to the first. e.g. 5 - (4) = 5 + (-4) = 1; -2 – 3 = -2 + (-3) = -5

PP1 Subtract -10 - (-5) = -10 + 5 = -5 (576)

PP2 Subtract (576)

a) 5 - 12 = 5 + (-12) = -7 b) -11 - 17 = -11 + (-17) = -28

PP3 Subtract (577)

a) 3.6 - (-9.5) = 3.6 + 9.5 = 13.1 b) -5/8 - (-5/24) = -15/24 + 5/24 = -10/24 = -5/12

Remember

The first number doesn’t change

The subtraction is changed to addition

We write the additive inverse for the second number

We find the result of the addition

PP4 Subtract (577)

a) 20 – (-5) = 20 + 5 = 25 b) -1/5 - (-1/2) = -2/10 + 5/10 = 3/10 c) 3.6 – (-5.5) = 3.5 + 5.5 = 9.1

9.2.2 Solving Problems Involving Both Addition and Subtraction of Signed Numbers (578)

OOO - Order of Operations

PP5 Perform the following operations (578)

-5 - (-9) + (-14)

-5 + 9 + (-14)

4 + (-14)

-10

9.2.3 Solving Simple Applied Problems That Involve the Subtraction of Signed Numbers

DayHgt of River (Ft above normal)

Mon -4

Tue -2a) What is the difference in height from Monday to Tuesday

Wed+5b) What is the difference in height from Tuesday to Wednesday

Thu+8 difference is the new - old

a) -2 - (-4) = -2 + 4 = 2 rose two feet

b) 5 - (-2) = 5 + 2 = 7 rose seven feet

PP6 Find the difference in temperature between 31F during the day and -37F at night

31 - ( -37) = 31 + 37 = 68 68 degrees F difference