Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 4 Quadratic Functions and Factoring - 4.7 Complete the Square - 4.7 Exercises - Skill Practice - Page 288: 38



Work Step by Step

The area of a trapezoid is the product of half the sum of the bases and its height. Hence here: $0.5 (3x-1+x+9)x=20\\x(4x+8)=40\\x(x+2)=10\\x^2+2x-10=0\\(x+1)^2-1^2-10=0\\(x+1)^2=11\\x+1=\pm\sqrt{11}\\x=-1\pm\sqrt{11}$ But we know that $x$ is non-negative, thus $x=-1+\sqrt{11}$
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