Answer
$\dfrac{1}{49}$
Work Step by Step
If $4^x=7$, then $4^{-x}=\frac{1}{7}$ (because the power of $-1$ takes the reciprocal)
Then.
$4^{-2x}=(4^{-x})^2=\left(\frac{1}{7}\right)^2=\frac{1}{49}$
Precalculus (10th Edition)
by Sullivan, Michael
Published by
Pearson
ISBN 10:
0-32197-907-9
ISBN 13:
978-0-32197-907-0
Chapter 5 - Exponential and Logarithmic Functions - 5.3 One-to-One Functions; Inverse Functions - 5.3 Assess Your Understanding - Page 282: 83
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