One-Step Addition and Subtraction EquationsChapter 2 Lesson 3

Seventh Grade Math

Another Look at Mental Math Equations(On the number line)

x + 3 = 2 + 3 = 2

Where do you start so that when you move three to the right you end at 2?

x + -2 = -5 Think, where do you start so that when you

move two to the left you end at -5?

Solving Equations is all about OPPOSITES! If you want to find where you started from on the

number line, you have to move in the opposite direction.

INVERSE OPERATIONS: Mathematical operations that “undo” each other Addition/subtraction Multiplication/division

Examples Using Inverse Operations

+ 2 = 10

THINK: The opposite of +2 is -2 10 – 2 = 8

GOLDEN RULE OF ALGEBRA

Whatever you do to one side of the equation,you must do to the other!

Balance Scale

Properties of EqualityAddition Property of Equality

If a = b then a + c = b + c

Subtraction Property of Equality If a = b then a - c = b - c

Easy Examples Using Inverse Operations to Solve One-Step Addition and Subtraction Equations1) x + 5 = 20 2) y + 8 = 16 3) j + 11 = 60

4) x – 33 = 50 5) y – 14 = 40 6) j – 10 = 23

Kicking it up a notch…

1) x + -2 = -6 2) y + 7 = 3 3) j + 3 = -2

4) v – 5 = -2 5) J – 3 = -10 6) y – (-4) = 12

1) Draw a line down your equal sign to make Sure you are keeping your equation balanced.2) Show all work (even if you can do it in your head!)3) Watch all sign rules4) Always use substitution to check your answer!

White Board Practice SHOW ALL WORK! Circle your solution.

1. x + 4 = 18

2. x – 5 = 20

3. x + 1.2 = 4

4. x – 4.3 = 6.3

5. y + 55 = 110

6. J – 30 = 53

7. x + 22 = 40

8. x – 220 = 500

White Board Practice With Negatives

x + -3 = 10

y + -5 = 15

j + -10 = -4

m + -30 = -12

x + 10 = -4

y + 20 = -12

s + 12 = -8

x + -9 = -21

White Board Practice With Negatives(sub)x – 7 = -3

y – 11 = -15

j – 22 = -6

x – (-3) = 5

y – (-6) = 33

k – (-20) = 25

m – (-3) = -5

x – (-9) = -24

Error Analysis- Correct and Explain the Mistakes

1) x + 23 = -5 2) y – (-4) = 20

23 + -5 = 18 The opposite of subtraction is addition

x = 18 20 + 4 = 24

3) j – 15 = -3 4) x + -24 = -22

The opposite of -3 is +3 The opposite of addition is subtraction

-15 + 3 = -12 -22 - 24 = -22 + -24

j = -12 x = -46