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Section 6.2 Solving Linear Equations Math in Our World

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Learning Objectives Decide if a number is a solution of an equation. Identify linear equations. Solve general linear equations. Solve linear equations containing fractions. Solve formulas for one specific variable. Determine if an equation is an identity or a contradiction.

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Equations An equation is a statement that two algebraic expressions are equal. A solution of an equation is a value of the variable that makes the equation a true statement when substituted into the equation. Solving an equation means finding every solution of the equation. We call the set of all solutions the solution set, or simply the solution of an equation. For example, x = 2 is one solution of the equation x 2 – 4 = 0, because (2) 2 – 4 = 0 is a true statement. But x = 2 is not the solution, because x = – 2 is a solution as well. The solution set is actually {– 2, 2}.

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Expressions vs. Equations Note the difference between the two; equations contain an equal sign and expressions do not.

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EXAMPLE 1 Identifying Solutions of an Equation Determine if the given value is a solution of the equation. (a) 4(x – 1) = 8; x = 2 (b) x + 7 = 2x – 1; x = 8 (c) 2y 2 = 200; y = – 10

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Linear Equations A linear equation does not break the following rules: *variables do not contain exponents greater than 1 *variables are not square rooted *variables do not appear in the denominator of a fraction *variables are not multiplied together

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EXAMPLE 2 Identifying Linear Equations Determine which of the equations below are linear equations.

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Solving Linear Equations One-step Equations *Addition/Subtraction Properties *Multiplication/Division Properties

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EXAMPLE 3 Solving Linear Equations Solve each equation using the Addition and Subtraction Property, and check your answer. (a) x – 5 = 9 (b) y + 30 = 110

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EXAMPLE 4 Solving Linear Equations Solve each equation using the Multiplication and Division Property, and check your answer.

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Solving Linear Equations Multi-step Equations Procedures for Solving Linear Equations Step 1 Simplify the expressions on both sides of the equation by distributing and combining like terms. Step 2 Get the term with the variable by itself using the addition or subtraction properties Step 3 Use the multiplication or division properties to solve for the variable.

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EXAMPLE 5 Solving a Linear Equation Solve the equation 5x + 9 = 29.

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EXAMPLE 6 Solving a Linear Equation Solve the equation 6x – 10 = 4x + 8.

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EXAMPLE 7 Solving a Linear Equation Solve the equation 3(2x + 5) – 10 = 3x – 10.

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Solving Equations Containing Fractions There’s a simple procedure that will turn any equation with fractions into one with no fractions at all. You just need to find the Least Common Denominator of all fractions that appear in the equation, and multiply every single term on each side of the equation by the LCD. If there are any fractions left after doing so, you made a mistake!

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EXAMPLE 8 Solving Linear Equations Containing Fractions Solve the equation:

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EXAMPLE 9 Solving Linear Equations Containing Fractions Solve the equation:

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Solve formulas for one specific variable.

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EXAMPLE 10 Solving a Formula in Electronics for One Variable Solve the formula

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EXAMPLE 11 Finding a Formula for Temperature in Celsius The formula F = 95 C + 32 gives the Fahrenheit equivalent for a temperature in Celsius. Transform this into a formula for calculating the Celsius temperature C.

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Contradictions and Identities A contradiction is an equation with no solution. An identity is an equation that is true for any value of the variable for which both sides are defined. When you solve an equation that is an identity, the final equation will be a statement that is always true. In a contradiction the final equation will be a statement that is false.

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EXAMPLE 12 Recognizing Identities and Contradictions Indicate whether the equation is an identity or a contradiction, and give the solution set. (a) 3(x – 6) + 2x = 5x – 18 (b) 6x – 4 + 2x = 8x – 10

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Classwork p : 7-71 eoo, 75, 77, 83

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