Answer
$8$ feet
Work Step by Step
Let $I$ be the intensity of light.
$I=\frac{k}{x^2}$
$I=80; x=2$
$80=\frac{k}{(2)^2}$
$k=320$
$I=\frac{320}{x^2}$
$I=5$
$5=\frac{320}{x^2}$
$x^2=\frac{320}{5}$
$x^2=64$
$x=8$ feet
Algebra: A Combined Approach (4th Edition)
by Martin-Gay, Elayn
Published by
Pearson
ISBN 10:
0321726391
ISBN 13:
978-0-32172-639-1
Chapter 9 - Section 9.4 - Variation and Problem Solving - Exercise Set - Page 665: 43
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