7th Grade Math

A zero pair is a number paired with its opposite, like 2 and -2. You

can add or subtract a zero pair from either side of an equation

without changing its value, because the value of a zero pair is zero.

Solve x + 2 = -1 using models.

Model the equation.

1

1

• 1

Y =

x + 2 = - 1

Add 2 negative tiles

• 1 - 1

Y =

1

• 1


• 1

1 - 1

x + 2 + (- 2 ) = - 1 + (- 2 )

to the left side of the

mat and add 2 negative

tiles to the right side

of the mat to form

zero pairs on the left.

Remove all of the zero

x = - 3

• 1


• 1

1

1

• 1


• 1

Y = -^1

pairs from the left side.

There are 3 negative

tiles on the right side

of the mat.

Therefore, x = -3.

Check Since - 3 + 2 = -1, the solution is correct. 

Lesson 1C Addition and Subtraction Equations 207

and Apply

Solve each equation using algebra tiles.

1. x + 4 = 4 2. 5 = x + 4 3. 4 = 1 + x 4. 2 = 2 + x


2. 
   
   
   
   • 2 = x + 1 6. x - 3 = - 2 7. x - 1 = - 3 8. 4 = x - 2
   
   
   
   


3. Explain how the work backward strategy is used to solve equations.


4. How is solving an equation similar to keeping a scale in balance?


5. MAKE A CONJECTURE Write a rule that you can use to solve an equation
   like x + 3 = 2 without using models or a drawing.


6. E WRITE MATH Write a real-world problem that can be solved using
   algebra tiles.

204_213_C04L1_895130.indd 207 12/31/09 3:55 PM