1. Solving Equations Using Addition and Subtraction
Algebra I Section 3.1

2. Think of an equation as having a left and right side
Think of an equation as having a left and right side. Each side is on a balanced scale
x + 3 = 5 x
1 1 1
1 1 1
1 1
If I remove the 3 ones from the left side, how to I keep the scale from tipping?

3. A. Equivalent Equations: equations that have the same solution.
Example:
x + 3 = 5
x = 5 – 3
x = 2

4. B. Isolating a variable: changing an equation to get the variable by itself on one side of the equation.
Example: x – 2 + (-4) = 12
x = 12 –
To isolate a variable, use inverse operations
Inverse Operations: Operations that undo each other. The inverse of addition is ________________. The inverse of multiplication is ______________.

5. x – 2 = 6 x + 5 = 7 x = 8+3 6 = x Ways to Isolate a Variable
a. Add a number to both sides
x – 2 = 6
b. Subtract a number from both sides
x + 5 = 7
c. Simplify
x = 8+3
d. Change sides
6 = x

6. C. Solution Steps: each step you take to isolate a variable
C. Solution Steps: each step you take to isolate a variable. (you must show these)
Examples:
State the inverse operations
Add 28
Subtract 15

7. Solve the equation (Show solution steps)
X = 4 – 7
t – 2 = 6
-9 = 2 + y

8. -3 + x = 7
r + 3⅟4 = 2⅟2
|-6|+ x = 11

9. 19 – (-y) = 25
x + 4 – 3 = 6 • 5
12 – 6 = -n

10. 4 = -b – 12
-r – (-7) = 16
Write an equation to represent the following problem. There are 15 members of a high school band brass section. After graduation there are only 7 members. How many members graduated?

11. Homework
Pg 135:18-44evens