Solve equations using addition and subtraction

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Slide 1

Solve equations using addition and subtraction

Objective The student will be able to:

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Designed by Skip Tyler, Varina High School

Slide 2

1) Solve r + 16 = -7

Think of this equation as a balance scale.

Whatever you do to one side has to be done to the other to keep it balanced!

Slide 3

1) Solve r + 16 = -7

To solve, you must get the variable by itself.

What number is on the same side as r?

16

To get r by itself, we must undo the “add 16”. What is the opposite of addition?

Subtract 16

Slide 4

- 16 -16

r = -23

-23 + 16 = -7

1) Solve r + 16 = -7

Draw “the river” to separate the equation into 2 sides

Subtract 16 from both sides

Simplify vertically

Check your answer by substituting your answer back into the problem

Slide 5

2) Solve x + 2 = -3 Get the variable by itself. What is your first step?

Add 2 to both sides

Subtract 2 from both sides

Add 3 to both sides

Subtract 3 from both sides

Slide 6

2) Solve x + 2 = -3

- 2 - 2

x = -5

-5 + 2 = -3

Draw “the river” to separate the equation into 2 sides

Subtract 2 from both sides

Simplify vertically

Check your answer by substituting your answer back into the problem

On homework and tests, be sure to check your work!!

There is no reason why you should miss a problem!

Slide 7

3) Solve 8 = m - 3

m = 5

m = 11

m = 24

m = 8/3

Slide 8

3) Solve 8 = m - 3

+ 3 + 3

11= m

8 = 11 - 3

Draw “the river” to separate the equation into 2 sides

Add 3 to both sides

Simplify vertically

Check your answer by substituting your answer back into the problem

Slide 9

When solving equations, we want to eliminate double signs.

y + (-3) = 8

is rewritten as

y – 3 = 8

p – (-5) = 6

is rewritten as

p + 5 = 6

As a general rule, replace “+ (- )” with “–” and “– (- )” with “+”. This will make things less confusing in the future!

Slide 10

4) Solve y + (-3) = 7

y – 3 = 7

+ 3 +3