Elementary Geometry for College Students (6th Edition)

Published by Brooks Cole
ISBN 10: 9781285195698
ISBN 13: 978-1-28519-569-8

Chapter 5 - Test - Page 264: 11a



Work Step by Step

$\triangle DEF$ is a 30-60-90 triangle. In this special triangle, the hypotenuse is twice the length of the shortest side (or the side opposite the $30^{\circ}$ angle). We are given that the hypotenuse is 10, or $FE=10$. $DE$ is the shortest side, or the side opposite the $40^{\circ}$ angle. So $DE$ is half the length of the hypotenuse, or $DE=5$.
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