a) \(\left|x\right|-15=6\Rightarrow\left|x\right|=21\Rightarrow\left[{}\begin{matrix}x=21\\x=-21\end{matrix}\right.\)
b) \(\left|x\right|+4=0\Rightarrow\left|x\right|=-4\Rightarrow x\in\varnothing\)
c) \(x^2-16=0\Rightarrow x^2=16=4^2\Rightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)
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a, /x/-15=6
/x/ =6+15
/x/ =21
x =\(\pm\)21
b, /x/+4=0
/x/ =0-4
/x/ =-4
x =4
c, x^2-16=0
x^2 =0+16
x^2 =16
x^2 = (\(\pm\)4)^2
x =\(\pm\) 4
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