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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 />

Problem 5 WORKED EXAMPLE<strong>–</strong>SOLVE QUADRATIC EQUNS BY TRIAL/ERROR<br />

FACTORING<br />

Use the Trial and Error Factoring Method to solve each of the quadratic equations below. Verify<br />

your result by graphing the quadratic part of the equation and looking at where it crosses the x-<br />

axis.<br />

a) Solve x 2 + x - 6 = 0<br />

Step 1: Make sure the equation is in standard form (check!).<br />

Step 2: Can we use GCF method? If no common factor other than one then no (can’t use<br />

here).<br />

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

Factor x 2 + x <strong>–</strong> 6 = (x + 3)(x <strong>–</strong> 2)<br />

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

Check: (x + 3)(x <strong>–</strong> 2) = x 2 <strong>–</strong> 2x + 3x <strong>–</strong> 6<br />

= x 2 + x <strong>–</strong> 6 (checks!)<br />

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

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

x = -3 or x = 2 are the solutions to x 2 + x <strong>–</strong> 6 = 0. Can also write as x = -3, 2<br />

Note: Graph x 2 + x - 6 and verify it crosses the x-axis at -3 and at 2.<br />

b) Solve x 2 <strong>–</strong> 4x <strong>–</strong> 32 = 0<br />

Step 1: In standard form (check!).<br />

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

Scottsdale Community College Page 216 <strong>Intermediate</strong> <strong>Algebra</strong>

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