Solving Equations with the Variable on Both Sides

Objectives:

• to solve equations with the variable on both sides.

To solve these equations,

•Use the addition or subtraction property to move all variables to one side of the equal sign.

•Then follow the steps to solving equations

Let’s see a few examples:

1) 6x - 3 = 2x + 13

-2x -2x

4x - 3 = 13

+3 +3

4x = 16

4 4

x = 4

Be sure to check your answer!

6(4) - 3 =? 2(4) + 13

24 - 3 =? 8 + 13

21 = 21

Let’s try another!

2) 3n + 1 = 7n - 5

-3n -3n

1 = 4n - 5

+5 +5

6 = 4n

4 4

Reduce! 3 = n

2

Check:

3(1.5) + 1 =? 7(1.5) - 5

4.5 + 1 =? 10.5 - 5

5.5 = 5.5

Here’s a tricky one!

3) 5 + 2(y + 4) = 5(y - 3) + 10• Distribute first.

5 + 2y + 8 = 5y - 15 + 10• Next, combine like terms.

2y + 13 = 5y - 5• Now solve. (Subtract 2y.)

13 = 3y - 5 (Add 5.)

18 = 3y (Divide by 3.)

6 = y

Check:

5 + 2(6 + 4) =? 5(6 - 3) + 10

5 + 2(10) =? 5(3) + 10

5 + 20 =? 15 + 10

25 = 25

Let’s try one with fractions!4)

3 - 2x = 4x - 6

3 = 6x - 6

9 = 6x so x = 3/2

3

8

1

4x

1

2x

3

4Steps:•Multiply each termby the least common denominator (8) to eliminate fractions.

•Solve for x.•Add 2x.•Add 6.•Divide by 6.

(8)3

8 (8)

1

4x(8)

1

2x (8)

3

4

Two special cases:

6(4 + y) - 3 = 4(y - 3) + 2y

24 + 6y - 3 = 4y - 12 + 2y

21 + 6y = 6y - 12

- 6y - 6y

21 = -12 Never true!

21 ≠ -12 NO SOLUTION!

3(a + 1) - 5 = 3a - 2

3a + 3 - 5 = 3a - 2

3a - 2 = 3a - 2

-3a -3a

-2 = -2 Always true!

We write IDENTITY.

Try a few on your own:

• 9x + 7 = 3x - 5

• 8 - 2(y + 1) = -3y + 1

• 8 - 1 z = 1 z - 7

2 4

The answers:

• x = -2

• y = -5

• z = 20