Answer
$3$
Work Step by Step
$\sqrt {12-x}=x$,
$12-x=x^2$,
$x^2+x-12=0$,
$(x+4)(x-3)=0$,
thus $x=-4, 3$,
check, only $x=3$ fits.
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
Published by
Pearson
ISBN 10:
0-32193-104-1
ISBN 13:
978-0-32193-104-7
Appendix A - Review - A.8 Solving Equations - A.8 Assess Your Understanding - Page A70: 52
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