Section 1.8 solving add sub equations (math)

Section 1.8Solving

Addition and Subtraction Equations

Which word do you think “Equation” has a connection

to?

YOU’RE CORRECT!

An equation is a

mathematical sentence

that contains an equal sign.

The part on the left side of the equal sign has the same value as the part on the right side. One or

both sides may contain a variable.

What is a variable?

A. A number that changes constantly.

B. A letter or symbol that stands for a number.

C. A number that varies as you move away from zero.

YOU’RE CORRECT!

A variable is a letter or

symbol that stands for a

number.

To solve an equation, you

must find what the variable

represents so that the two

parts are equal.

Equations are like balance scales. In order to keep a scale balanced you must have the same amount of weight on both sides.

If I took one block away from the left side, what would I have to do to keep

the scale from tipping?

If I added 6 more apples to the right side, how could I keep the scale from

tipping?

To keep an equation equal,

we must do exactly the same thing to each side

of the equation. If we add a number to one side, we

must add that same number to the other side

and vice versa.

Addition and subtraction are called “opposite

operations” because they can ‘undo’

each other.

What are the other two opposite

operations?

Multiplication and division are opposite operations,

too!

for Solving Addition and Subtraction Equations

1. Look to see what side the

variable is on.

2. Decide what

operation is being shown.

3. Do the opposite of

that operation to both sides.

4. Write what

number the variable

stands for (ex: a = 2).

5. Check the solution by “plugging” the number back into the equation to see if the sides are equal.

Example 1m + 18 = 34 Look for variable

-18 -18 Do the opposite

m = 16 Write what m is

m + 18 = 34

16 + 18 = 34 Plug in m

34 = 34 Solution is correct!

If you check your solution and you do

not come out with the same numbers, then your solution is not correct. Therefore,

you must rework the problem.

Always check your answers to equations.

It is the only way to make sure you get a

problem correct. Why miss a problem when

you can get all of them correct?

Example 2 68 = y + 43 Look for variable

-43 -43 Do the opposite

25 = y Write what y is

68 = y + 43

68 = 25 + 43 Plug in y

68 = 68 Solution is correct!

Example 3 t - 14 = 22 Look for variable

+ 14 +14 Do the opposite

t = 36 Write what t is

t - 14 = 22

36 - 14 = 22 Plug in t

22 = 22 Solution is correct!

Try These...1. r + 5 = 18

2. m - 26 = 59

3. 102 = x - 15

4. a + 39 = 56

r = 13

m = 85

117 = x

a = 17

Let’s do Checking for

Understanding Page 47 # 4 - 9

Prediction:You will show all of the

steps (including checking) as you have been shown today or

credit will not be given for your homework.

Are there any questions

about solving addition or subtraction equations?

Homework:

Page 48 12-34 even

Don’t forget to check your solution!