Find roots of polynomial $$ p(x) = -r^3+40r+128 $$
Answer
The roots of polynomial $ p(r) $ are:
$$ \begin{aligned}r_1 &= 7.5472\\[1 em]r_2 &= -3.7736+1.6492i\\[1 em]r_3 &= -3.7736-1.6492i \end{aligned} $$Explanation
Polynomial $ -r^3+40r+128 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.
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