The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4\\[1 em]x_2 &= -4 \end{aligned} $$Step 1:
Write polynomial in descending order
$$ \begin{aligned} 16-x^2 & = 0\\[1 em] -x^2+16 & = 0 \end{aligned} $$Step 2:
The solutions of $ -x^2+16 = 0 $ are: $ x = -4 ~ \text{and} ~ x = 4$.
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