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Intermediate Algebra – Student Workbook – Second Edition 2013

Intermediate Algebra – Student Workbook – Second Edition 2013

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Lesson 5b - Solving Quadratic Equations<br />

Mini-Lesson<br />

Step 3: Try to factor the left side by Trial and Error<br />

Factor: x 2 <strong>–</strong> 4x <strong>–</strong> 32 = (x <strong>–</strong> 8)(x + 4)<br />

Check by Foiling to be sure your answer is correct.<br />

Check: (x <strong>–</strong> 8)(x + 4) = x 2 + 4x <strong>–</strong> 8x <strong>–</strong> 32<br />

= x 2 <strong>–</strong> 4x <strong>–</strong> 32 (checks!)<br />

Step 4: Write the factored form of the quadratic then set each factor to 0 and solve for x.<br />

(x <strong>–</strong> 8)(x + 4)= 0 so x <strong>–</strong> 8 = 0 or x + 4 = 0.<br />

Solutions to x 2 <strong>–</strong> 4x <strong>–</strong> 32 = 0 are x = 8, -4.<br />

Note:<br />

Verify by graphing.<br />

c) Solve 2x 2 + 7x =15<br />

Step 1: Convert the equation to Standard Form<br />

Step 2: No GCF other than 1 (check!).<br />

Step 3: Try to factor the left side by Trial and Error<br />

Factor: 2x 2 + 7x <strong>–</strong> 15 = (2x <strong>–</strong> 3)(x + 5)<br />

Check by Foiling.<br />

( )( )<br />

Step 4: Write the factored form of the quadratic then set each factor to 0 and solve for x.<br />

(2x <strong>–</strong> 3)(x + 5)= 0 so 2x <strong>–</strong> 3 = 0 or x + 5 = 0.<br />

Solutions to 2x 2 + 7x =15 are x = 3/2, -5.<br />

Verify by graphing.<br />

Scottsdale Community College Page 217 <strong>Intermediate</strong> <strong>Algebra</strong>

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