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Big Ideas Math: Modeling Real Life, Grade 7

BI

Big Ideas Math: Modeling Real Life, Grade 7 View details

3. Solving Two-Step Equations

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Exercise 3 Page 140

Start by adding 12 to both sides.

x=7

Practice makes perfect

To solve an equation, we should first gather all of the variable terms on one side and all of the constant terms on the other side using the Properties of Equality. In this case, the only variable term is already on the right-hand side of the equation, so we will start by adding 12 to both sides.

9=3x-12

LHS+12=RHS+12

9+12=3x-12+12

Add terms

21=3x

.LHS /3.=.RHS /3.

21/3 = 3x/3

Calculate quotient

7=x

Rearrange equation

x=7

The solution to the equation is x=7. We can check our solution by substituting it into the original equation.

9=3x-12

x= 7

9 ? = 3( 7)-12

Multiply

9 ? = 21-12

Subtract term

9=9

Since the left-hand side is equal to the right-hand side, our solution is correct.

Subchapter links

Try It p.140-141

Self-Assessment for Concept & Skills p.141

Self-Assessment for Problem Solving p.142

Review & Refresh p.143

Concept, Skills, & Problem Solving p.143-144